Ordinary Di erential Equations. Session 2roquesol/Math_308_Fall_2017... · 2017-09-12 · Linear and Nonlinear Equations Theorem 1 (Existence and Uniqueness). Suppose p(t) and g(t)

Linear and Nonlinear EquationsModeling

Ordinary Differential Equations. Session 2

Dr. Marco A Roque Sol

17/01/2017

Dr. Marco A Roque Sol Ordinary Differential Equations. Session 2

Linear and Nonlinear Equations

Theorem 1 (Existence and Uniqueness).

Suppose p(t) and g(t) are continuous real-valued functions on aninterval (α, β) that contains the point t0. Then, for any choice of(initial value) y0, there exists a unique solution y(t) on the wholeinterval (α, β) to the linear differential equation

dy(t)

dt+ p(t)y(t) = g(t)

for all t ∈ (α, β) and y(t0) = yo.




Suppose p(t) and g(t)

are continuous real-valued functions on aninterval (α, β) that contains the point t0. Then, for any choice of(initial value) y0, there exists a unique solution y(t) on the wholeinterval (α, β) to the linear differential equation

dy(t)

dt+ p(t)y(t) = g(t)





Suppose p(t) and g(t) are continuous real-valued functions on aninterval (α, β)

that contains the point t0. Then, for any choice of(initial value) y0, there exists a unique solution y(t) on the wholeinterval (α, β) to the linear differential equation

dy(t)

dt+ p(t)y(t) = g(t)





Suppose p(t) and g(t) are continuous real-valued functions on aninterval (α, β) that contains the point t0.

Then, for any choice of(initial value) y0, there exists a unique solution y(t) on the wholeinterval (α, β) to the linear differential equation

dy(t)

dt+ p(t)y(t) = g(t)





Suppose p(t) and g(t) are continuous real-valued functions on aninterval (α, β) that contains the point t0. Then, for any choice of(initial value) y0,

there exists a unique solution y(t) on the wholeinterval (α, β) to the linear differential equation

dy(t)

dt+ p(t)y(t) = g(t)





Suppose p(t) and g(t) are continuous real-valued functions on aninterval (α, β) that contains the point t0. Then, for any choice of(initial value) y0, there exists a unique solution y(t)

on the wholeinterval (α, β) to the linear differential equation

dy(t)

dt+ p(t)y(t) = g(t)





Suppose p(t) and g(t) are continuous real-valued functions on aninterval (α, β) that contains the point t0. Then, for any choice of(initial value) y0, there exists a unique solution y(t) on the wholeinterval (α, β)

to the linear differential equation

dy(t)

dt+ p(t)y(t) = g(t)






dy(t)

dt+ p(t)y(t) = g(t)






dy(t)

dt+ p(t)y(t) = g(t)






dy(t)

dt+ p(t)y(t) = g(t)






dy(t)

dt+ p(t)y(t) = g(t)





Suppose that both f (t, y) and∂f

∂y(t, y) are continuous functions

defined on a region R as

R = {(t, y) : t0 − δ < t < t0 + δ; y0 − ε < y < y0 + ε}

containing the point (t0, y0). Then there exists a number δ1(possibly smaller than δ) so that a solution y = f (t) to

y ′ = f (t, y) y(t0) = y0

is the unique solution for t0 − δ1 < t < t0 + δ1




Suppose that both f (t, y)

and∂f



R = {(t, y) : t0 − δ < t < t0 + δ; y0 − ε < y < y0 + ε}


y ′ = f (t, y) y(t0) = y0






∂y(t, y)

are continuous functions


R = {(t, y) : t0 − δ < t < t0 + δ; y0 − ε < y < y0 + ε}


y ′ = f (t, y) y(t0) = y0








R = {(t, y) : t0 − δ < t < t0 + δ; y0 − ε < y < y0 + ε}


y ′ = f (t, y) y(t0) = y0








R = {(t, y) : t0 − δ < t < t0 + δ; y0 − ε < y < y0 + ε}


y ′ = f (t, y) y(t0) = y0








R = {(t, y) : t0 − δ < t < t0 + δ; y0 − ε < y < y0 + ε}

containing the point (t0, y0).

Then there exists a number δ1(possibly smaller than δ) so that a solution y = f (t) to

y ′ = f (t, y) y(t0) = y0








R = {(t, y) : t0 − δ < t < t0 + δ; y0 − ε < y < y0 + ε}

containing the point (t0, y0). Then there exists a number δ1(possibly smaller than δ)

so that a solution y = f (t) to

y ′ = f (t, y) y(t0) = y0








R = {(t, y) : t0 − δ < t < t0 + δ; y0 − ε < y < y0 + ε}


y ′ = f (t, y) y(t0) = y0








R = {(t, y) : t0 − δ < t < t0 + δ; y0 − ε < y < y0 + ε}


y ′ = f (t, y) y(t0) = y0








R = {(t, y) : t0 − δ < t < t0 + δ; y0 − ε < y < y0 + ε}


y ′ = f (t, y) y(t0) = y0

is the unique solution

for t0 − δ1 < t < t0 + δ1







R = {(t, y) : t0 − δ < t < t0 + δ; y0 − ε < y < y0 + ε}


y ′ = f (t, y) y(t0) = y0








R = {(t, y) : t0 − δ < t < t0 + δ; y0 − ε < y < y0 + ε}


y ′ = f (t, y) y(t0) = y0




Example 21

Consider the ODE

y ′ = t − y + 1; y(1) = 2

In this case, both the function f (t, y) = ty + 1 and its partial

derivative∂f

∂y(t, y) = −1 are defined and continuous at all points

(x , y). The Theorem 2 guarantees that a solution to the ODEexists in some open interval centered at 1, and that this solution isunique in some (possibly smaller) interval centered at 1.



Example 21

Consider the ODE

y ′ = t − y + 1; y(1) = 2


derivative∂f





Example 21

Consider the ODE

y ′ = t − y + 1; y(1) = 2


derivative∂f





Example 21

Consider the ODE

y ′ = t − y + 1; y(1) = 2

In this case,

both the function f (t, y) = ty + 1 and its partial

derivative∂f





Example 21

Consider the ODE

y ′ = t − y + 1; y(1) = 2

In this case, both the function f (t, y) = ty + 1

and its partial

derivative∂f





Example 21

Consider the ODE

y ′ = t − y + 1; y(1) = 2


derivative∂f

∂y(t, y) = −1

are defined and continuous at all points




Example 21

Consider the ODE

y ′ = t − y + 1; y(1) = 2


derivative∂f


(x , y).

The Theorem 2 guarantees that a solution to the ODEexists in some open interval centered at 1, and that this solution isunique in some (possibly smaller) interval centered at 1.



Example 21

Consider the ODE

y ′ = t − y + 1; y(1) = 2


derivative∂f


(x , y). The Theorem 2 guarantees

that a solution to the ODEexists in some open interval centered at 1, and that this solution isunique in some (possibly smaller) interval centered at 1.



Example 21

Consider the ODE

y ′ = t − y + 1; y(1) = 2


derivative∂f


(x , y). The Theorem 2 guarantees that a solution to the ODEexists

in some open interval centered at 1, and that this solution isunique in some (possibly smaller) interval centered at 1.



Example 21

Consider the ODE

y ′ = t − y + 1; y(1) = 2


derivative∂f


(x , y). The Theorem 2 guarantees that a solution to the ODEexists in some open interval centered at 1,

and that this solution isunique in some (possibly smaller) interval centered at 1.



Example 21

Consider the ODE

y ′ = t − y + 1; y(1) = 2


derivative∂f


(x , y). The Theorem 2 guarantees that a solution to the ODEexists in some open interval centered at 1, and that this solution isunique

in some (possibly smaller) interval centered at 1.



Example 21

Consider the ODE

y ′ = t − y + 1; y(1) = 2


derivative∂f





Example 21

Consider the ODE

y ′ = t − y + 1; y(1) = 2


derivative∂f





In fact, an explicit solution to this equation is

y(t) = t + e1t

This solution exists (and is the unique solution to the equation) forall real numbers t. In other words, in this example we may choosethe numbers δ and δ1 as large as we please.

Example 22

Consider the ODE

y ′ = 1 + y2; y(0) = 0




y(t) = t + e1t


Example 22

Consider the ODE

y ′ = 1 + y2; y(0) = 0




y(t) = t + e1t

This solution exists (and is the unique solution to the equation) forall real numbers t.

In other words, in this example we may choosethe numbers δ and δ1 as large as we please.

Example 22

Consider the ODE

y ′ = 1 + y2; y(0) = 0




y(t) = t + e1t

This solution exists (and is the unique solution to the equation) forall real numbers t. In other words,

in this example we may choosethe numbers δ and δ1 as large as we please.

Example 22

Consider the ODE

y ′ = 1 + y2; y(0) = 0




y(t) = t + e1t

This solution exists (and is the unique solution to the equation) forall real numbers t. In other words, in this example we may choosethe numbers δ and δ1

as large as we please.

Example 22

Consider the ODE

y ′ = 1 + y2; y(0) = 0




y(t) = t + e1t


Example 22

Consider the ODE

y ′ = 1 + y2; y(0) = 0




y(t) = t + e1t


Example 22

Consider the ODE

y ′ = 1 + y2; y(0) = 0




y(t) = t + e1t


Example 22

Consider the ODE

y ′ = 1 + y2; y(0) = 0




y(t) = t + e1t


Example 22

Consider the ODE

y ′ = 1 + y2; y(0) = 0




y(t) = t + e1t


Example 22

Consider the ODE

y ′ = 1 + y2; y(0) = 0



In this case, both the function f (t, y) = 1 + y2

and its partial

derivative∂f

∂y(t, y) = 2y are defined and continuous at all points

(t, y).

The Theorem 2 guarantees that a solution to the ODE exists insome open interval centered at 0, and that this solution is uniquein some (possibly smaller) interval centered at 1.

By separating variables and integrating, we derive a solution to thisequation of the form

y(t) = tan(t)



In this case, both the function f (t, y) = 1 + y2 and its partial

derivative∂f

∂y(t, y) = 2y

are defined and continuous at all points

(t, y).



y(t) = tan(t)




derivative∂f

∂y(t, y) = 2y are defined and continuous

at all points

(t, y).



y(t) = tan(t)




derivative∂f


(t, y).



y(t) = tan(t)




derivative∂f


(t, y).

The Theorem 2 guarantees

that a solution to the ODE exists insome open interval centered at 0, and that this solution is uniquein some (possibly smaller) interval centered at 1.


y(t) = tan(t)




derivative∂f


(t, y).

The Theorem 2 guarantees that a solution to the ODE exists

insome open interval centered at 0, and that this solution is uniquein some (possibly smaller) interval centered at 1.


y(t) = tan(t)




derivative∂f


(t, y).

The Theorem 2 guarantees that a solution to the ODE exists insome open interval centered at 0,

and that this solution is uniquein some (possibly smaller) interval centered at 1.


y(t) = tan(t)




derivative∂f


(t, y).

The Theorem 2 guarantees that a solution to the ODE exists insome open interval centered at 0, and that this solution is unique

in some (possibly smaller) interval centered at 1.


y(t) = tan(t)




derivative∂f


(t, y).



y(t) = tan(t)




derivative∂f


(t, y).


By separating variables and integrating,

we derive a solution to thisequation of the form

y(t) = tan(t)




derivative∂f


(t, y).



y(t) = tan(t)




derivative∂f


(t, y).



y(t) = tan(t)




derivative∂f


(t, y).



y(t) = tan(t)



As an abstract function of t,

this is defined for allt 6= ...,−3π/2,−π/2, π/2, 3π/2, ... However, in order for thisfunction to be considered as a solution to this ODE, we mustrestrict the domain. Specifically, the function

y(t) = tan(t); −π/2 < x < π/2

is a solution to the above ODE. In this example we must chooseδ1 = π/2, although the initial value δ, may be chosen as large aswe please.



As an abstract function of t, this is defined for allt 6= ...,−3π/2,−π/2, π/2, 3π/2, ...

However, in order for thisfunction to be considered as a solution to this ODE, we mustrestrict the domain. Specifically, the function

y(t) = tan(t); −π/2 < x < π/2




As an abstract function of t, this is defined for allt 6= ...,−3π/2,−π/2, π/2, 3π/2, ... However, in order for thisfunction to be considered as a solution to this ODE, we mustrestrict the domain.

Specifically, the function

y(t) = tan(t); −π/2 < x < π/2




As an abstract function of t, this is defined for allt 6= ...,−3π/2,−π/2, π/2, 3π/2, ... However, in order for thisfunction to be considered as a solution to this ODE, we mustrestrict the domain. Specifically, the function

y(t) = tan(t); −π/2 < x < π/2





y(t) = tan(t); −π/2 < x < π/2





y(t) = tan(t); −π/2 < x < π/2

is a solution to the above ODE.

In this example we must chooseδ1 = π/2, although the initial value δ, may be chosen as large aswe please.




y(t) = tan(t); −π/2 < x < π/2

is a solution to the above ODE. In this example we must chooseδ1 = π/2,

although the initial value δ, may be chosen as large aswe please.




y(t) = tan(t); −π/2 < x < π/2

is a solution to the above ODE. In this example we must chooseδ1 = π/2, although the initial value δ,

may be chosen as large aswe please.




y(t) = tan(t); −π/2 < x < π/2





y(t) = tan(t); −π/2 < x < π/2



Modeling

We now move into one of the main applications of differentialequations.

Modeling is the process of writing a differential equation todescribe a physical situation. Almost all of the differentialequations that you will use in your job are there becausesomebody, at some time, modeled a situation to come up with thedifferential equation that you are using.

This section is designed to introduce you to the process ofmodeling and show you what is involved in modeling.


Modeling


Modeling is the process of writing a differential equation todescribe a physical situation.

Almost all of the differentialequations that you will use in your job are there becausesomebody, at some time, modeled a situation to come up with thedifferential equation that you are using.



Modeling


Modeling is the process of writing a differential equation todescribe a physical situation. Almost all of the differentialequations

that you will use in your job are there becausesomebody, at some time, modeled a situation to come up with thedifferential equation that you are using.



Modeling


Modeling is the process of writing a differential equation todescribe a physical situation. Almost all of the differentialequations that you will use in your job

are there becausesomebody, at some time, modeled a situation to come up with thedifferential equation that you are using.



Modeling


Modeling is the process of writing a differential equation todescribe a physical situation. Almost all of the differentialequations that you will use in your job are there becausesomebody, at some time,

modeled a situation to come up with thedifferential equation that you are using.



Modeling


Modeling is the process of writing a differential equation todescribe a physical situation. Almost all of the differentialequations that you will use in your job are there becausesomebody, at some time, modeled a situation to come up with thedifferential equation

that you are using.



Modeling





Modeling



This section is designed to introduce you to the process ofmodeling

and show you what is involved in modeling.


Modeling





Modeling





Modeling

Mixing Problems

In these problems we will start with a substance that is dissolved ina liquid. Liquid will be entering and leaving a holding tank.

The liquid entering the tank may or may not contain more of thesubstance dissolved in it. Liquid leaving the tank will of coursecontain the substance dissolved in it.

If Q(t) gives the amount of the substance dissolved in the liquid inthe tank at any time t we want to develop a differential equationthat, when solved, will give us an expression for Q(t) .


Modeling

Mixing Problems

In these problems we will start

with a substance that is dissolved ina liquid. Liquid will be entering and leaving a holding tank.




Modeling

Mixing Problems

In these problems we will start with a substance that is dissolved ina liquid.

Liquid will be entering and leaving a holding tank.




Modeling

Mixing Problems





Modeling

Mixing Problems


The liquid entering the tank

may or may not contain more of thesubstance dissolved in it. Liquid leaving the tank will of coursecontain the substance dissolved in it.



Modeling

Mixing Problems


The liquid entering the tank may or may not

contain more of thesubstance dissolved in it. Liquid leaving the tank will of coursecontain the substance dissolved in it.



Modeling

Mixing Problems


The liquid entering the tank may or may not contain more of thesubstance dissolved in it.

Liquid leaving the tank will of coursecontain the substance dissolved in it.



Modeling

Mixing Problems


The liquid entering the tank may or may not contain more of thesubstance dissolved in it. Liquid leaving the tank

will of coursecontain the substance dissolved in it.



Modeling

Mixing Problems





Modeling

Mixing Problems



If Q(t)

gives the amount of the substance dissolved in the liquid inthe tank at any time t we want to develop a differential equationthat, when solved, will give us an expression for Q(t) .


Modeling

Mixing Problems



If Q(t) gives the amount of the substance

dissolved in the liquid inthe tank at any time t we want to develop a differential equationthat, when solved, will give us an expression for Q(t) .


Modeling

Mixing Problems



If Q(t) gives the amount of the substance dissolved in the liquid inthe tank at any time t

we want to develop a differential equationthat, when solved, will give us an expression for Q(t) .


Modeling

Mixing Problems



If Q(t) gives the amount of the substance dissolved in the liquid inthe tank at any time t we want to develop a differential equationthat, when solved,

will give us an expression for Q(t) .


Modeling

Mixing Problems





Modeling

Mixing Problems





Modeling

Note as well that in many situations

we can think of air as a liquidfor the purposes of these kinds of discussions and so we dontactually need to have an actual liquid, but could instead use air asthe liquid.

The main assumption that well be using here is that theconcentration of the substance in the liquid is uniform throughoutthe tank. Clearly this will not be the case, but if we allow theconcentration to vary depending on the location in the tank, theproblem becomes very difficult.


Modeling

Note as well that in many situations we can think of air as a liquidfor the purposes of these kinds of discussions

and so we dontactually need to have an actual liquid, but could instead use air asthe liquid.



Modeling

Note as well that in many situations we can think of air as a liquidfor the purposes of these kinds of discussions and so we dontactually need to have an actual liquid,

but could instead use air asthe liquid.



Modeling

Note as well that in many situations we can think of air as a liquidfor the purposes of these kinds of discussions and so we dontactually need to have an actual liquid, but could instead use air asthe liquid.



Modeling


The main assumption that well be using here

is that theconcentration of the substance in the liquid is uniform throughoutthe tank. Clearly this will not be the case, but if we allow theconcentration to vary depending on the location in the tank, theproblem becomes very difficult.


Modeling


The main assumption that well be using here is that theconcentration of the substance in the liquid

is uniform throughoutthe tank. Clearly this will not be the case, but if we allow theconcentration to vary depending on the location in the tank, theproblem becomes very difficult.


Modeling


The main assumption that well be using here is that theconcentration of the substance in the liquid is uniform throughoutthe tank.

Clearly this will not be the case, but if we allow theconcentration to vary depending on the location in the tank, theproblem becomes very difficult.


Modeling


The main assumption that well be using here is that theconcentration of the substance in the liquid is uniform throughoutthe tank. Clearly this will not be the case,

but if we allow theconcentration to vary depending on the location in the tank, theproblem becomes very difficult.


Modeling


The main assumption that well be using here is that theconcentration of the substance in the liquid is uniform throughoutthe tank. Clearly this will not be the case, but if we allow theconcentration to vary depending on the location in the tank,

theproblem becomes very difficult.


Modeling




Modeling




Modeling

The main equation that well be using to model this situation is :

Rate of change of Q(t) =

Rate at which Q(t) enters the tank -

Rate at which Q(t) exits the tank

where,

Rate of change of Q(t) =dQ(t)

dt= Q(t)′


Modeling





where,


dt= Q(t)′


Modeling





where,


dt= Q(t)′


Modeling





where,


dt= Q(t)′


Modeling





where,


dt= Q(t)′


Modeling





where,


dt= Q(t)′


Modeling





where,


dt= Q(t)′


Modeling

Rate at which Q(t) enters the tank = (flow rate of liquid entering)x (concentration of substance in liquid entering)

Rate at which Q(t) exits the tank = (flow rate of liquid exiting) x(concentration of substance in liquid exiting)

Let’s take a look at the first problem


Modeling





Modeling





Modeling





Modeling

Example 14

A 1500 gallon tank initially contains 600 gallons of water with 5lbs of salt dissolved in it.

Water enters the tank at a rate of 9gal/hr and the water entering the tank has a salt concentration of15 (1 + cos(t)) lbs/gal. If a well mixed solution leaves the tank at arate of 6 gal/hr, how much salt is in the tank when it overflows?

We are going to assume that the instant the water enters the tankit somehow instantly disperses evenly throughout the tank to givea uniform concentration of salt in the tank at every point. Again,this will clearly not be the case in reality, but it will allow us to dothe problem.


Modeling

Example 14

A 1500 gallon tank initially contains 600 gallons of water with 5lbs of salt dissolved in it. Water enters the tank at a rate of 9gal/hr and the water entering the tank

has a salt concentration of15 (1 + cos(t)) lbs/gal. If a well mixed solution leaves the tank at arate of 6 gal/hr, how much salt is in the tank when it overflows?



Modeling

Example 14

A 1500 gallon tank initially contains 600 gallons of water with 5lbs of salt dissolved in it. Water enters the tank at a rate of 9gal/hr and the water entering the tank has a salt concentration of15 (1 + cos(t)) lbs/gal.

If a well mixed solution leaves the tank at arate of 6 gal/hr, how much salt is in the tank when it overflows?



Modeling

Example 14

A 1500 gallon tank initially contains 600 gallons of water with 5lbs of salt dissolved in it. Water enters the tank at a rate of 9gal/hr and the water entering the tank has a salt concentration of15 (1 + cos(t)) lbs/gal. If a well mixed solution leaves the tank at arate of 6 gal/hr,

how much salt is in the tank when it overflows?



Modeling

Example 14

A 1500 gallon tank initially contains 600 gallons of water with 5lbs of salt dissolved in it. Water enters the tank at a rate of 9gal/hr and the water entering the tank has a salt concentration of15 (1 + cos(t)) lbs/gal. If a well mixed solution leaves the tank at arate of 6 gal/hr, how much salt is in the tank when it overflows?



Modeling

Example 14


We are going to assume that the instant the water

enters the tankit somehow instantly disperses evenly throughout the tank to givea uniform concentration of salt in the tank at every point. Again,this will clearly not be the case in reality, but it will allow us to dothe problem.


Modeling

Example 14


We are going to assume that the instant the water enters the tankit somehow instantly disperses evenly throughout the tank

to givea uniform concentration of salt in the tank at every point. Again,this will clearly not be the case in reality, but it will allow us to dothe problem.


Modeling

Example 14


We are going to assume that the instant the water enters the tankit somehow instantly disperses evenly throughout the tank to givea uniform concentration of salt in the tank at every point.

Again,this will clearly not be the case in reality, but it will allow us to dothe problem.


Modeling

Example 14


We are going to assume that the instant the water enters the tankit somehow instantly disperses evenly throughout the tank to givea uniform concentration of salt in the tank at every point. Again,this will clearly not be the case in reality,

but it will allow us to dothe problem.


Modeling

Example 14




Modeling

Example 14




Modeling

Solution

Now, to set up the IVP that we will need to solve to get Q(t) wewill need the flow rate of the water entering, the concentration ofthe salt in the water entering, the flow rate of the water leaving(weve got that) and the concentration of the salt in the waterexiting (we dont have this )

Since we are assuming a uniform concentration of salt in the tankthe concentration at any point in the tank and hence in the waterexiting is given by,

Concentration = (Amount of salt in the tank at any time t) / (Volume of water in the tank at any time t)


Modeling

Solution

Now,

to set up the IVP that we will need to solve to get Q(t) wewill need the flow rate of the water entering, the concentration ofthe salt in the water entering, the flow rate of the water leaving(weve got that) and the concentration of the salt in the waterexiting (we dont have this )




Modeling

Solution

Now, to set up the IVP that we will need to solve to get Q(t)

wewill need the flow rate of the water entering, the concentration ofthe salt in the water entering, the flow rate of the water leaving(weve got that) and the concentration of the salt in the waterexiting (we dont have this )




Modeling

Solution

Now, to set up the IVP that we will need to solve to get Q(t) wewill need the flow rate of the water entering,

the concentration ofthe salt in the water entering, the flow rate of the water leaving(weve got that) and the concentration of the salt in the waterexiting (we dont have this )




Modeling

Solution

Now, to set up the IVP that we will need to solve to get Q(t) wewill need the flow rate of the water entering, the concentration ofthe salt in the water entering,

the flow rate of the water leaving(weve got that) and the concentration of the salt in the waterexiting (we dont have this )




Modeling

Solution

Now, to set up the IVP that we will need to solve to get Q(t) wewill need the flow rate of the water entering, the concentration ofthe salt in the water entering, the flow rate of the water leaving(weve got that) and

the concentration of the salt in the waterexiting (we dont have this )




Modeling

Solution





Modeling

Solution


Since we are assuming a uniform concentration of salt in the tank

the concentration at any point in the tank and hence in the waterexiting is given by,



Modeling

Solution


Since we are assuming a uniform concentration of salt in the tankthe concentration at any point in the tank

and hence in the waterexiting is given by,



Modeling

Solution





Modeling

Solution





Modeling

Solution





Modeling

The amount at any time t is easy it’s just Q(t).

The volume isalso pretty easy. We start with 600 gallons and every hour 9gallons enters and 6 gallons leave. So, if we use t in hours, everyhour 3 gallons enters the tank, or at any time t there is 600 + 3tgallons of water in the tank.

So, the IVP for this situation is,

Q ′(t) = (9)

(1

5(1 + cos(t))

)− 6

(Q(t)

600 + 3t

)Q(0) = 5

Q ′(t) =9

5(1 + cos(t))− 2

(Q(t)

200 + t

)Q(0) = 5


Modeling

The amount at any time t is easy it’s just Q(t). The volume isalso pretty easy.

We start with 600 gallons and every hour 9gallons enters and 6 gallons leave. So, if we use t in hours, everyhour 3 gallons enters the tank, or at any time t there is 600 + 3tgallons of water in the tank.


Q ′(t) = (9)

(1

5(1 + cos(t))

)− 6

(Q(t)

600 + 3t

)Q(0) = 5

Q ′(t) =9

5(1 + cos(t))− 2

(Q(t)

200 + t

)Q(0) = 5


Modeling

The amount at any time t is easy it’s just Q(t). The volume isalso pretty easy. We start with 600 gallons

and every hour 9gallons enters and 6 gallons leave. So, if we use t in hours, everyhour 3 gallons enters the tank, or at any time t there is 600 + 3tgallons of water in the tank.


Q ′(t) = (9)

(1

5(1 + cos(t))

)− 6

(Q(t)

600 + 3t

)Q(0) = 5

Q ′(t) =9

5(1 + cos(t))− 2

(Q(t)

200 + t

)Q(0) = 5


Modeling

The amount at any time t is easy it’s just Q(t). The volume isalso pretty easy. We start with 600 gallons and every hour 9gallons enters

and 6 gallons leave. So, if we use t in hours, everyhour 3 gallons enters the tank, or at any time t there is 600 + 3tgallons of water in the tank.


Q ′(t) = (9)

(1

5(1 + cos(t))

)− 6

(Q(t)

600 + 3t

)Q(0) = 5

Q ′(t) =9

5(1 + cos(t))− 2

(Q(t)

200 + t

)Q(0) = 5


Modeling

The amount at any time t is easy it’s just Q(t). The volume isalso pretty easy. We start with 600 gallons and every hour 9gallons enters and 6 gallons leave.

So, if we use t in hours, everyhour 3 gallons enters the tank, or at any time t there is 600 + 3tgallons of water in the tank.


Q ′(t) = (9)

(1

5(1 + cos(t))

)− 6

(Q(t)

600 + 3t

)Q(0) = 5

Q ′(t) =9

5(1 + cos(t))− 2

(Q(t)

200 + t

)Q(0) = 5


Modeling

The amount at any time t is easy it’s just Q(t). The volume isalso pretty easy. We start with 600 gallons and every hour 9gallons enters and 6 gallons leave. So, if we use t in hours,

everyhour 3 gallons enters the tank, or at any time t there is 600 + 3tgallons of water in the tank.


Q ′(t) = (9)

(1

5(1 + cos(t))

)− 6

(Q(t)

600 + 3t

)Q(0) = 5

Q ′(t) =9

5(1 + cos(t))− 2

(Q(t)

200 + t

)Q(0) = 5


Modeling

The amount at any time t is easy it’s just Q(t). The volume isalso pretty easy. We start with 600 gallons and every hour 9gallons enters and 6 gallons leave. So, if we use t in hours, everyhour 3 gallons enters the tank,

or at any time t there is 600 + 3tgallons of water in the tank.


Q ′(t) = (9)

(1

5(1 + cos(t))

)− 6

(Q(t)

600 + 3t

)Q(0) = 5

Q ′(t) =9

5(1 + cos(t))− 2

(Q(t)

200 + t

)Q(0) = 5


Modeling

The amount at any time t is easy it’s just Q(t). The volume isalso pretty easy. We start with 600 gallons and every hour 9gallons enters and 6 gallons leave. So, if we use t in hours, everyhour 3 gallons enters the tank, or at any time t

there is 600 + 3tgallons of water in the tank.


Q ′(t) = (9)

(1

5(1 + cos(t))

)− 6

(Q(t)

600 + 3t

)Q(0) = 5

Q ′(t) =9

5(1 + cos(t))− 2

(Q(t)

200 + t

)Q(0) = 5


Modeling

The amount at any time t is easy it’s just Q(t). The volume isalso pretty easy. We start with 600 gallons and every hour 9gallons enters and 6 gallons leave. So, if we use t in hours, everyhour 3 gallons enters the tank, or at any time t there is 600 + 3tgallons of water in the tank.


Q ′(t) = (9)

(1

5(1 + cos(t))

)− 6

(Q(t)

600 + 3t

)Q(0) = 5

Q ′(t) =9

5(1 + cos(t))− 2

(Q(t)

200 + t

)Q(0) = 5


Modeling



Q ′(t) = (9)

(1

5(1 + cos(t))

)− 6

(Q(t)

600 + 3t

)Q(0) = 5

Q ′(t) =9

5(1 + cos(t))− 2

(Q(t)

200 + t

)Q(0) = 5


Modeling



Q ′(t) = (9)

(1

5(1 + cos(t))

)− 6

(Q(t)

600 + 3t

)Q(0) = 5

Q ′(t) =9

5(1 + cos(t))− 2

(Q(t)

200 + t

)Q(0) = 5


Modeling



Q ′(t) = (9)

(1

5(1 + cos(t))

)− 6

(Q(t)

600 + 3t

)Q(0) = 5

Q ′(t) =9

5(1 + cos(t))− 2

(Q(t)

200 + t

)Q(0) = 5


Modeling



Q ′(t) = (9)

(1

5(1 + cos(t))

)− 6

(Q(t)

600 + 3t

)Q(0) = 5

Q ′(t) =9

5(1 + cos(t))− 2

(Q(t)

200 + t

)Q(0) = 5


Modeling

This is a linear differential equation.

We will show most of thedetails, but leave the description of the solution process out.

Q ′(t) +

(2

Q(t)

200 + t

)=

9

5(1 + cos(t))

Now find the integrating factor:

µ(t) = e∫

2200+t

dt = e2ln(200+t) = e ln(200+t)2 = (200 + t)2

Now, multiply the rewritten differential equationby the integratingfactor.

(200 + t)2Q ′(t) + (200 + t)2(

2Q(t)

200 + t

)= (200 + t)2

9

5(1 + cos(t))


Modeling

This is a linear differential equation. We will show most of thedetails, but leave the description of the solution process out.

Q ′(t) +

(2

Q(t)

200 + t

)=

9

5(1 + cos(t))


µ(t) = e∫

2200+t

dt = e2ln(200+t) = e ln(200+t)2 = (200 + t)2


(200 + t)2Q ′(t) + (200 + t)2(

2Q(t)

200 + t

)= (200 + t)2

9

5(1 + cos(t))


Modeling


Q ′(t) +

(2

Q(t)

200 + t

)=

9

5(1 + cos(t))


µ(t) = e∫

2200+t

dt = e2ln(200+t) = e ln(200+t)2 = (200 + t)2


(200 + t)2Q ′(t) + (200 + t)2(

2Q(t)

200 + t

)= (200 + t)2

9

5(1 + cos(t))


Modeling


Q ′(t) +

(2

Q(t)

200 + t

)=

9

5(1 + cos(t))


µ(t) = e∫

2200+t

dt = e2ln(200+t) = e ln(200+t)2 = (200 + t)2


(200 + t)2Q ′(t) + (200 + t)2(

2Q(t)

200 + t

)= (200 + t)2

9

5(1 + cos(t))


Modeling


Q ′(t) +

(2

Q(t)

200 + t

)=

9

5(1 + cos(t))


µ(t) = e∫

2200+t

dt = e2ln(200+t) = e ln(200+t)2 = (200 + t)2

Now,

multiply the rewritten differential equationby the integratingfactor.

(200 + t)2Q ′(t) + (200 + t)2(

2Q(t)

200 + t

)= (200 + t)2

9

5(1 + cos(t))


Modeling


Q ′(t) +

(2

Q(t)

200 + t

)=

9

5(1 + cos(t))


µ(t) = e∫

2200+t

dt = e2ln(200+t) = e ln(200+t)2 = (200 + t)2

Now, multiply the rewritten differential equation

by the integratingfactor.

(200 + t)2Q ′(t) + (200 + t)2(

2Q(t)

200 + t

)= (200 + t)2

9

5(1 + cos(t))


Modeling


Q ′(t) +

(2

Q(t)

200 + t

)=

9

5(1 + cos(t))


µ(t) = e∫

2200+t

dt = e2ln(200+t) = e ln(200+t)2 = (200 + t)2


(200 + t)2Q ′(t) + (200 + t)2(

2Q(t)

200 + t

)= (200 + t)2

9

5(1 + cos(t))


Modeling


Q ′(t) +

(2

Q(t)

200 + t

)=

9

5(1 + cos(t))


µ(t) = e∫

2200+t

dt = e2ln(200+t) = e ln(200+t)2 = (200 + t)2


(200 + t)2Q ′(t) + (200 + t)2(

2Q(t)

200 + t

)= (200 + t)2

9

5(1 + cos(t))


Modeling


Q ′(t) +

(2

Q(t)

200 + t

)=

9

5(1 + cos(t))


µ(t) = e∫

2200+t

dt = e2ln(200+t) = e ln(200+t)2 = (200 + t)2


(200 + t)2Q ′(t) + (200 + t)2(

2Q(t)

200 + t

)= (200 + t)2

9

5(1 + cos(t))


Modeling

((200 + t)2Q(t)

)′= (200 + t)2

9

5(1 + cos(t))

Integrate both sides and solve for the solution.∫ ((200 + t)2Q(t)

)′dt =

∫9

5(200 + t)2 (1 + cos(t)) dt

(200 + t)2Q(t) =9

5[1

3(200 + t)3 + (200 + t)2sin(t) + ...

...+ 2(200 + t)cos(t)− 2sin(t)] + c

Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)+

c

(200 + t)2


Modeling

((200 + t)2Q(t)

)′= (200 + t)2

9

5(1 + cos(t))

Integrate both sides and solve for the solution.

∫ ((200 + t)2Q(t)

)′dt =

∫9

5(200 + t)2 (1 + cos(t)) dt

(200 + t)2Q(t) =9

5[1

3(200 + t)3 + (200 + t)2sin(t) + ...

...+ 2(200 + t)cos(t)− 2sin(t)] + c

Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)+

c

(200 + t)2


Modeling

((200 + t)2Q(t)

)′= (200 + t)2

9

5(1 + cos(t))


)′dt =

∫9

5(200 + t)2 (1 + cos(t)) dt

(200 + t)2Q(t) =9

5[1

3(200 + t)3 + (200 + t)2sin(t) + ...

...+ 2(200 + t)cos(t)− 2sin(t)] + c

Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)+

c

(200 + t)2


Modeling

((200 + t)2Q(t)

)′= (200 + t)2

9

5(1 + cos(t))


)′dt =

∫9

5(200 + t)2 (1 + cos(t)) dt

(200 + t)2Q(t) =9

5[1

3(200 + t)3 + (200 + t)2sin(t) + ...

...+ 2(200 + t)cos(t)− 2sin(t)] + c

Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)+

c

(200 + t)2


Modeling

((200 + t)2Q(t)

)′= (200 + t)2

9

5(1 + cos(t))


)′dt =

∫9

5(200 + t)2 (1 + cos(t)) dt

(200 + t)2Q(t) =9

5[1

3(200 + t)3 + (200 + t)2sin(t) + ...

...+ 2(200 + t)cos(t)− 2sin(t)] + c

Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)+

c

(200 + t)2


Modeling

((200 + t)2Q(t)

)′= (200 + t)2

9

5(1 + cos(t))


)′dt =

∫9

5(200 + t)2 (1 + cos(t)) dt

(200 + t)2Q(t) =9

5[1

3(200 + t)3 + (200 + t)2sin(t) + ...

...+ 2(200 + t)cos(t)− 2sin(t)] + c

Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)+

c

(200 + t)2


Modeling

((200 + t)2Q(t)

)′= (200 + t)2

9

5(1 + cos(t))


)′dt =

∫9

5(200 + t)2 (1 + cos(t)) dt

(200 + t)2Q(t) =9

5[1

3(200 + t)3 + (200 + t)2sin(t) + ...

...+ 2(200 + t)cos(t)− 2sin(t)] + c

Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)+

c

(200 + t)2


Modeling

And applying initial conditions

5 = Q(0) =9

5

(1

3(200) +

2

200

)+

c

(200)2

c = −4600720

The solution is then,

Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)− 4600720

(200 + t)2

Now, the tank will overflow at t = 300hrs. The amount of salt inthe tank at that time is.

Q(300) = 279.80lbs


Modeling


5 = Q(0) =9

5

(1

3(200) +

2

200

)+

c

(200)2

c = −4600720


Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)− 4600720

(200 + t)2


Q(300) = 279.80lbs


Modeling


5 = Q(0) =9

5

(1

3(200) +

2

200

)+

c

(200)2

c = −4600720


Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)− 4600720

(200 + t)2


Q(300) = 279.80lbs


Modeling


5 = Q(0) =9

5

(1

3(200) +

2

200

)+

c

(200)2

c = −4600720


Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)− 4600720

(200 + t)2


Q(300) = 279.80lbs


Modeling


5 = Q(0) =9

5

(1

3(200) +

2

200

)+

c

(200)2

c = −4600720


Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)− 4600720

(200 + t)2


Q(300) = 279.80lbs


Modeling


5 = Q(0) =9

5

(1

3(200) +

2

200

)+

c

(200)2

c = −4600720


Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)− 4600720

(200 + t)2


Q(300) = 279.80lbs


Modeling


5 = Q(0) =9

5

(1

3(200) +

2

200

)+

c

(200)2

c = −4600720


Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)− 4600720

(200 + t)2


Q(300) = 279.80lbs


Modeling


5 = Q(0) =9

5

(1

3(200) +

2

200

)+

c

(200)2

c = −4600720


Q(t) =9

5

(1

3(200 + t)2 + sin(t) +

2cos(t)

200 + t− 2sin(t)

(200 + t)2

)− 4600720

(200 + t)2


Q(300) = 279.80lbs


Modeling


Modeling

Example 15

A 1000 gallon holding tank that catches runoff from some chemicalprocess initially has 800 gallons of water with 2 ounces of pollutiondissolved in it. Polluted water flows into the tank at a rate of 3gal/hr and contains 5 ounces/gal of pollution in it. A well mixedsolution leaves the tank at 3 gal/hr as well. When the amount ofpollution in the holding tank reaches 500 ounces the inflow ofpolluted water is cut off and fresh water will enter the tank at adecreased rate of 2 gal/hr while the outflow is increased to 4gal/hr.Determine the amount of pollution in the tank at any time t.


Modeling

Example 15

A 1000 gallon holding tank

that catches runoff from some chemicalprocess initially has 800 gallons of water with 2 ounces of pollutiondissolved in it. Polluted water flows into the tank at a rate of 3gal/hr and contains 5 ounces/gal of pollution in it. A well mixedsolution leaves the tank at 3 gal/hr as well. When the amount ofpollution in the holding tank reaches 500 ounces the inflow ofpolluted water is cut off and fresh water will enter the tank at adecreased rate of 2 gal/hr while the outflow is increased to 4gal/hr.Determine the amount of pollution in the tank at any time t.


Modeling

Example 15

A 1000 gallon holding tank that catches runoff from some chemicalprocess initially has 800 gallons of water

with 2 ounces of pollutiondissolved in it. Polluted water flows into the tank at a rate of 3gal/hr and contains 5 ounces/gal of pollution in it. A well mixedsolution leaves the tank at 3 gal/hr as well. When the amount ofpollution in the holding tank reaches 500 ounces the inflow ofpolluted water is cut off and fresh water will enter the tank at adecreased rate of 2 gal/hr while the outflow is increased to 4gal/hr.Determine the amount of pollution in the tank at any time t.


Modeling

Example 15

A 1000 gallon holding tank that catches runoff from some chemicalprocess initially has 800 gallons of water with 2 ounces of pollutiondissolved in it.

Polluted water flows into the tank at a rate of 3gal/hr and contains 5 ounces/gal of pollution in it. A well mixedsolution leaves the tank at 3 gal/hr as well. When the amount ofpollution in the holding tank reaches 500 ounces the inflow ofpolluted water is cut off and fresh water will enter the tank at adecreased rate of 2 gal/hr while the outflow is increased to 4gal/hr.Determine the amount of pollution in the tank at any time t.


Modeling

Example 15

A 1000 gallon holding tank that catches runoff from some chemicalprocess initially has 800 gallons of water with 2 ounces of pollutiondissolved in it. Polluted water flows into the tank at a rate of 3gal/hr

and contains 5 ounces/gal of pollution in it. A well mixedsolution leaves the tank at 3 gal/hr as well. When the amount ofpollution in the holding tank reaches 500 ounces the inflow ofpolluted water is cut off and fresh water will enter the tank at adecreased rate of 2 gal/hr while the outflow is increased to 4gal/hr.Determine the amount of pollution in the tank at any time t.


Modeling

Example 15

A 1000 gallon holding tank that catches runoff from some chemicalprocess initially has 800 gallons of water with 2 ounces of pollutiondissolved in it. Polluted water flows into the tank at a rate of 3gal/hr and contains 5 ounces/gal of pollution in it.

A well mixedsolution leaves the tank at 3 gal/hr as well. When the amount ofpollution in the holding tank reaches 500 ounces the inflow ofpolluted water is cut off and fresh water will enter the tank at adecreased rate of 2 gal/hr while the outflow is increased to 4gal/hr.Determine the amount of pollution in the tank at any time t.


Modeling

Example 15

A 1000 gallon holding tank that catches runoff from some chemicalprocess initially has 800 gallons of water with 2 ounces of pollutiondissolved in it. Polluted water flows into the tank at a rate of 3gal/hr and contains 5 ounces/gal of pollution in it. A well mixedsolution

leaves the tank at 3 gal/hr as well. When the amount ofpollution in the holding tank reaches 500 ounces the inflow ofpolluted water is cut off and fresh water will enter the tank at adecreased rate of 2 gal/hr while the outflow is increased to 4gal/hr.Determine the amount of pollution in the tank at any time t.


Modeling

Example 15

A 1000 gallon holding tank that catches runoff from some chemicalprocess initially has 800 gallons of water with 2 ounces of pollutiondissolved in it. Polluted water flows into the tank at a rate of 3gal/hr and contains 5 ounces/gal of pollution in it. A well mixedsolution leaves the tank at 3 gal/hr as well.

When the amount ofpollution in the holding tank reaches 500 ounces the inflow ofpolluted water is cut off and fresh water will enter the tank at adecreased rate of 2 gal/hr while the outflow is increased to 4gal/hr.Determine the amount of pollution in the tank at any time t.


Modeling

Example 15

A 1000 gallon holding tank that catches runoff from some chemicalprocess initially has 800 gallons of water with 2 ounces of pollutiondissolved in it. Polluted water flows into the tank at a rate of 3gal/hr and contains 5 ounces/gal of pollution in it. A well mixedsolution leaves the tank at 3 gal/hr as well. When the amount ofpollution in the holding tank reaches 500 ounces the inflow ofpolluted water is cut off

and fresh water will enter the tank at adecreased rate of 2 gal/hr while the outflow is increased to 4gal/hr.Determine the amount of pollution in the tank at any time t.


Modeling

Example 15

A 1000 gallon holding tank that catches runoff from some chemicalprocess initially has 800 gallons of water with 2 ounces of pollutiondissolved in it. Polluted water flows into the tank at a rate of 3gal/hr and contains 5 ounces/gal of pollution in it. A well mixedsolution leaves the tank at 3 gal/hr as well. When the amount ofpollution in the holding tank reaches 500 ounces the inflow ofpolluted water is cut off and fresh water will enter the tank at adecreased rate of 2 gal/hr

while the outflow is increased to 4gal/hr.Determine the amount of pollution in the tank at any time t.


Modeling

Example 15

A 1000 gallon holding tank that catches runoff from some chemicalprocess initially has 800 gallons of water with 2 ounces of pollutiondissolved in it. Polluted water flows into the tank at a rate of 3gal/hr and contains 5 ounces/gal of pollution in it. A well mixedsolution leaves the tank at 3 gal/hr as well. When the amount ofpollution in the holding tank reaches 500 ounces the inflow ofpolluted water is cut off and fresh water will enter the tank at adecreased rate of 2 gal/hr while the outflow is increased to 4gal/hr.

Determine the amount of pollution in the tank at any time t.


Modeling

Example 15



Modeling

Example 15



Modeling

Solution

The pollution in the tank will increase as time passes. If theamount of pollution ever reaches the maximum allowed there willbe a change in the situation.

This will necessitate a change in the differential equationdescribing the process as well. In other words, we’ll need two IVP’sfor this problem. One will describe the initial situation whenpolluted runoff is entering the tank and one for after the maximumallowed pollution is reached and fresh water is entering the tank.

Here are the two IVPs for this problem.

Q ′1(t) = (3)(5)− 3

(Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm


Modeling

Solution

The pollution in the tank will increase as time passes.

If theamount of pollution ever reaches the maximum allowed there willbe a change in the situation.



Q ′1(t) = (3)(5)− 3

(Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm


Modeling

Solution

The pollution in the tank will increase as time passes. If theamount of pollution ever reaches the maximum allowed

there willbe a change in the situation.



Q ′1(t) = (3)(5)− 3

(Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm


Modeling

Solution




Q ′1(t) = (3)(5)− 3

(Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm


Modeling

Solution


This will necessitate a change in the differential equationdescribing the process as well.

In other words, we’ll need two IVP’sfor this problem. One will describe the initial situation whenpolluted runoff is entering the tank and one for after the maximumallowed pollution is reached and fresh water is entering the tank.


Q ′1(t) = (3)(5)− 3

(Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm


Modeling

Solution


This will necessitate a change in the differential equationdescribing the process as well. In other words, we’ll need two IVP’sfor this problem.

One will describe the initial situation whenpolluted runoff is entering the tank and one for after the maximumallowed pollution is reached and fresh water is entering the tank.


Q ′1(t) = (3)(5)− 3

(Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm


Modeling

Solution


This will necessitate a change in the differential equationdescribing the process as well. In other words, we’ll need two IVP’sfor this problem. One will describe the initial situation

whenpolluted runoff is entering the tank and one for after the maximumallowed pollution is reached and fresh water is entering the tank.


Q ′1(t) = (3)(5)− 3

(Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm


Modeling

Solution


This will necessitate a change in the differential equationdescribing the process as well. In other words, we’ll need two IVP’sfor this problem. One will describe the initial situation whenpolluted runoff is entering the tank

and one for after the maximumallowed pollution is reached and fresh water is entering the tank.


Q ′1(t) = (3)(5)− 3

(Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm


Modeling

Solution


This will necessitate a change in the differential equationdescribing the process as well. In other words, we’ll need two IVP’sfor this problem. One will describe the initial situation whenpolluted runoff is entering the tank and one for after the maximumallowed pollution is reached

and fresh water is entering the tank.


Q ′1(t) = (3)(5)− 3

(Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm


Modeling

Solution




Q ′1(t) = (3)(5)− 3

(Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm


Modeling

Solution




Q ′1(t) = (3)(5)− 3

(Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm


Modeling

Solution




Q ′1(t) = (3)(5)− 3

(Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm


Modeling

Solution




Q ′1(t) = (3)(5)− 3

(Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm


Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te

The first one is fairly straight forward and will be valid until themaximum amount of pollution is reached. We’ll call that time tm.Also, the volume in the tank remains constant during this time sowe dont need to do anything fancy with that this time in thesecond term as we did in the previous example.

We will need a little explanation for the second one. First noticethat we do not start over at t = 0. We start this one at tm, thetime at which the new process starts. Next, fresh water is flowinginto the tank and so the concentration of pollution in the incomingwater is zero. This will drop out the first term, and thats okay sodon’t worry about that.


Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te

The first one is fairly straight forward

and will be valid until themaximum amount of pollution is reached. We’ll call that time tm.Also, the volume in the tank remains constant during this time sowe dont need to do anything fancy with that this time in thesecond term as we did in the previous example.



Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te

The first one is fairly straight forward and will be valid until themaximum amount of pollution is reached.

We’ll call that time tm.Also, the volume in the tank remains constant during this time sowe dont need to do anything fancy with that this time in thesecond term as we did in the previous example.



Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te

The first one is fairly straight forward and will be valid until themaximum amount of pollution is reached. We’ll call that time tm.

Also, the volume in the tank remains constant during this time sowe dont need to do anything fancy with that this time in thesecond term as we did in the previous example.



Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te

The first one is fairly straight forward and will be valid until themaximum amount of pollution is reached. We’ll call that time tm.Also, the volume in the tank remains constant during this time

sowe dont need to do anything fancy with that this time in thesecond term as we did in the previous example.



Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te

The first one is fairly straight forward and will be valid until themaximum amount of pollution is reached. We’ll call that time tm.Also, the volume in the tank remains constant during this time sowe dont need to do anything fancy

with that this time in thesecond term as we did in the previous example.



Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te

The first one is fairly straight forward and will be valid until themaximum amount of pollution is reached. We’ll call that time tm.Also, the volume in the tank remains constant during this time sowe dont need to do anything fancy with that this time in thesecond term

as we did in the previous example.



Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te




Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te


We will need a little explanation for the second one.

First noticethat we do not start over at t = 0. We start this one at tm, thetime at which the new process starts. Next, fresh water is flowinginto the tank and so the concentration of pollution in the incomingwater is zero. This will drop out the first term, and thats okay sodon’t worry about that.


Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te


We will need a little explanation for the second one. First noticethat we do not start over at t = 0.

We start this one at tm, thetime at which the new process starts. Next, fresh water is flowinginto the tank and so the concentration of pollution in the incomingwater is zero. This will drop out the first term, and thats okay sodon’t worry about that.


Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te


We will need a little explanation for the second one. First noticethat we do not start over at t = 0. We start this one at tm,

thetime at which the new process starts. Next, fresh water is flowinginto the tank and so the concentration of pollution in the incomingwater is zero. This will drop out the first term, and thats okay sodon’t worry about that.


Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te


We will need a little explanation for the second one. First noticethat we do not start over at t = 0. We start this one at tm, thetime at which the new process starts.

Next, fresh water is flowinginto the tank and so the concentration of pollution in the incomingwater is zero. This will drop out the first term, and thats okay sodon’t worry about that.


Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te


We will need a little explanation for the second one. First noticethat we do not start over at t = 0. We start this one at tm, thetime at which the new process starts. Next, fresh water is flowinginto the tank

and so the concentration of pollution in the incomingwater is zero. This will drop out the first term, and thats okay sodon’t worry about that.


Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te


We will need a little explanation for the second one. First noticethat we do not start over at t = 0. We start this one at tm, thetime at which the new process starts. Next, fresh water is flowinginto the tank and so the concentration of pollution in the incomingwater is zero.

This will drop out the first term, and thats okay sodon’t worry about that.


Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te


We will need a little explanation for the second one. First noticethat we do not start over at t = 0. We start this one at tm, thetime at which the new process starts. Next, fresh water is flowinginto the tank and so the concentration of pollution in the incomingwater is zero. This will drop out the first term,

and thats okay sodon’t worry about that.


Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te




Modeling

Q ′2(t) = (2)(0)− 4

(Q2(t)

800− 2(t − tm)

)Q(tm) = 500 tm ≤ t ≤ te




Modeling

Now,

notice that the volume at any time looks a little funny.During this time frame we are losing two gallons of water everyhour of the process so we need the − 2 in there to account forthat. However, we cant just use t as we did in the previousexample. When this new process starts upthere needs to be 800gallons of water in the tank and if we just use t there we won’thave the required 800 gallons that we need in the equation. So, tomake sure that we have the proper volume we need to put in thedifference in times. In this way once we are one hour into the newprocess (i.e t - tm = 1) we will have 798 gallons in the tank asrequired.


Modeling

Now, notice that the volume at any time looks a little funny.

During this time frame we are losing two gallons of water everyhour of the process so we need the − 2 in there to account forthat. However, we cant just use t as we did in the previousexample. When this new process starts upthere needs to be 800gallons of water in the tank and if we just use t there we won’thave the required 800 gallons that we need in the equation. So, tomake sure that we have the proper volume we need to put in thedifference in times. In this way once we are one hour into the newprocess (i.e t - tm = 1) we will have 798 gallons in the tank asrequired.


Modeling

Now, notice that the volume at any time looks a little funny.During this time frame we are losing two gallons of water everyhour of the process

so we need the − 2 in there to account forthat. However, we cant just use t as we did in the previousexample. When this new process starts upthere needs to be 800gallons of water in the tank and if we just use t there we won’thave the required 800 gallons that we need in the equation. So, tomake sure that we have the proper volume we need to put in thedifference in times. In this way once we are one hour into the newprocess (i.e t - tm = 1) we will have 798 gallons in the tank asrequired.


Modeling

Now, notice that the volume at any time looks a little funny.During this time frame we are losing two gallons of water everyhour of the process so we need the − 2 in there to account forthat.

However, we cant just use t as we did in the previousexample. When this new process starts upthere needs to be 800gallons of water in the tank and if we just use t there we won’thave the required 800 gallons that we need in the equation. So, tomake sure that we have the proper volume we need to put in thedifference in times. In this way once we are one hour into the newprocess (i.e t - tm = 1) we will have 798 gallons in the tank asrequired.


Modeling

Now, notice that the volume at any time looks a little funny.During this time frame we are losing two gallons of water everyhour of the process so we need the − 2 in there to account forthat. However, we cant just use t as we did in the previousexample.

When this new process starts upthere needs to be 800gallons of water in the tank and if we just use t there we won’thave the required 800 gallons that we need in the equation. So, tomake sure that we have the proper volume we need to put in thedifference in times. In this way once we are one hour into the newprocess (i.e t - tm = 1) we will have 798 gallons in the tank asrequired.


Modeling

Now, notice that the volume at any time looks a little funny.During this time frame we are losing two gallons of water everyhour of the process so we need the − 2 in there to account forthat. However, we cant just use t as we did in the previousexample. When this new process starts up

there needs to be 800gallons of water in the tank and if we just use t there we won’thave the required 800 gallons that we need in the equation. So, tomake sure that we have the proper volume we need to put in thedifference in times. In this way once we are one hour into the newprocess (i.e t - tm = 1) we will have 798 gallons in the tank asrequired.


Modeling

Now, notice that the volume at any time looks a little funny.During this time frame we are losing two gallons of water everyhour of the process so we need the − 2 in there to account forthat. However, we cant just use t as we did in the previousexample. When this new process starts upthere needs to be 800gallons of water in the tank

and if we just use t there we won’thave the required 800 gallons that we need in the equation. So, tomake sure that we have the proper volume we need to put in thedifference in times. In this way once we are one hour into the newprocess (i.e t - tm = 1) we will have 798 gallons in the tank asrequired.


Modeling

Now, notice that the volume at any time looks a little funny.During this time frame we are losing two gallons of water everyhour of the process so we need the − 2 in there to account forthat. However, we cant just use t as we did in the previousexample. When this new process starts upthere needs to be 800gallons of water in the tank and if we just use t there we won’thave the required 800 gallons

that we need in the equation. So, tomake sure that we have the proper volume we need to put in thedifference in times. In this way once we are one hour into the newprocess (i.e t - tm = 1) we will have 798 gallons in the tank asrequired.


Modeling

Now, notice that the volume at any time looks a little funny.During this time frame we are losing two gallons of water everyhour of the process so we need the − 2 in there to account forthat. However, we cant just use t as we did in the previousexample. When this new process starts upthere needs to be 800gallons of water in the tank and if we just use t there we won’thave the required 800 gallons that we need in the equation.

So, tomake sure that we have the proper volume we need to put in thedifference in times. In this way once we are one hour into the newprocess (i.e t - tm = 1) we will have 798 gallons in the tank asrequired.


Modeling

Now, notice that the volume at any time looks a little funny.During this time frame we are losing two gallons of water everyhour of the process so we need the − 2 in there to account forthat. However, we cant just use t as we did in the previousexample. When this new process starts upthere needs to be 800gallons of water in the tank and if we just use t there we won’thave the required 800 gallons that we need in the equation. So, tomake sure that we have the proper volume

we need to put in thedifference in times. In this way once we are one hour into the newprocess (i.e t - tm = 1) we will have 798 gallons in the tank asrequired.


Modeling

Now, notice that the volume at any time looks a little funny.During this time frame we are losing two gallons of water everyhour of the process so we need the − 2 in there to account forthat. However, we cant just use t as we did in the previousexample. When this new process starts upthere needs to be 800gallons of water in the tank and if we just use t there we won’thave the required 800 gallons that we need in the equation. So, tomake sure that we have the proper volume we need to put in thedifference in times.

In this way once we are one hour into the newprocess (i.e t - tm = 1) we will have 798 gallons in the tank asrequired.


Modeling

Now, notice that the volume at any time looks a little funny.During this time frame we are losing two gallons of water everyhour of the process so we need the − 2 in there to account forthat. However, we cant just use t as we did in the previousexample. When this new process starts upthere needs to be 800gallons of water in the tank and if we just use t there we won’thave the required 800 gallons that we need in the equation. So, tomake sure that we have the proper volume we need to put in thedifference in times. In this way once we are one hour into the newprocess (i.e t - tm = 1)

we will have 798 gallons in the tank asrequired.


Modeling

Now, notice that the volume at any time looks a little funny.During this time frame we are losing two gallons of water everyhour of the process so we need the − 2 in there to account forthat. However, we cant just use t as we did in the previousexample. When this new process starts upthere needs to be 800gallons of water in the tank and if we just use t there we won’thave the required 800 gallons that we need in the equation. So, tomake sure that we have the proper volume we need to put in thedifference in times. In this way once we are one hour into the newprocess (i.e t - tm = 1) we will have 798 gallons

in the tank asrequired.


Modeling

Now, notice that the volume at any time looks a little funny.During this time frame we are losing two gallons of water everyhour of the process so we need the − 2 in there to account forthat. However, we cant just use t as we did in the previousexample. When this new process starts upthere needs to be 800gallons of water in the tank and if we just use t there we won’thave the required 800 gallons that we need in the equation. So, tomake sure that we have the proper volume we need to put in thedifference in times. In this way once we are one hour into the newprocess (i.e t - tm = 1) we will have 798 gallons in the tank asrequired.


Modeling

Now, notice that the volume at any time looks a little funny.During this time frame we are losing two gallons of water everyhour of the process so we need the − 2 in there to account forthat. However, we cant just use t as we did in the previousexample. When this new process starts upthere needs to be 800gallons of water in the tank and if we just use t there we won’thave the required 800 gallons that we need in the equation. So, tomake sure that we have the proper volume we need to put in thedifference in times. In this way once we are one hour into the newprocess (i.e t - tm = 1) we will have 798 gallons in the tank asrequired.


Modeling

Finally, the second process can’t continue forever as eventually thetank will empty.

This is denoted in the time restrictions as te . Wecan also note that te = tm + 400 since the tank will empty 400hours after this new process starts up.

Well, it will end provided something doesn’t come along and startchanging the situation again.

Okay, now that we’ve got all the explanations taken care of here’sthe simplified version of the IVP’s that we’ll be solving.


Modeling

Finally, the second process can’t continue forever as eventually thetank will empty. This is denoted in the time restrictions as te .

Wecan also note that te = tm + 400 since the tank will empty 400hours after this new process starts up.




Modeling

Finally, the second process can’t continue forever as eventually thetank will empty. This is denoted in the time restrictions as te . Wecan also note that te = tm + 400

since the tank will empty 400hours after this new process starts up.




Modeling

Finally, the second process can’t continue forever as eventually thetank will empty. This is denoted in the time restrictions as te . Wecan also note that te = tm + 400 since the tank will empty

400hours after this new process starts up.




Modeling

Finally, the second process can’t continue forever as eventually thetank will empty. This is denoted in the time restrictions as te . Wecan also note that te = tm + 400 since the tank will empty 400hours after this new process starts up.




Modeling


Well,

it will end provided something doesn’t come along and startchanging the situation again.



Modeling


Well, it will end provided something doesn’t come along

and startchanging the situation again.



Modeling





Modeling



Okay,

now that we’ve got all the explanations taken care of here’sthe simplified version of the IVP’s that we’ll be solving.


Modeling



Okay, now that we’ve got all the explanations taken care of

here’sthe simplified version of the IVP’s that we’ll be solving.


Modeling





Modeling





Modeling

Q ′1(t) = 15−(

3Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm

Q ′2(t) = −(

2Q2(t)

400− (t − tm)

)Q(tm) = 500 tm ≤ t ≤ te

The first IVP is a fairly simple linear differential equation so we willleave the details of the solution to you to check.


Modeling

Q ′1(t) = 15−(

3Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm

Q ′2(t) = −(

2Q2(t)

400− (t − tm)

)Q(tm) = 500 tm ≤ t ≤ te



Modeling

Q ′1(t) = 15−(

3Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm

Q ′2(t) = −(

2Q2(t)

400− (t − tm)

)Q(tm) = 500 tm ≤ t ≤ te

The first IVP is a fairly simple linear differential equation

so we willleave the details of the solution to you to check.


Modeling

Q ′1(t) = 15−(

3Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm

Q ′2(t) = −(

2Q2(t)

400− (t − tm)

)Q(tm) = 500 tm ≤ t ≤ te



Modeling

Q ′1(t) = 15−(

3Q1(t)

800

)Q(0) = 2 0 ≤ t ≤ tm

Q ′2(t) = −(

2Q2(t)

400− (t − tm)

)Q(tm) = 500 tm ≤ t ≤ te



Modeling

Q1(t) = 4000− 3998e−3t800

Now, we need to find tm. We need to do is determine when theamount of pollution reaches 500. So we need to solve.

Q1(t) = 4000− 3998e−3t800 = 500

tm = 35.475

So, the second process will pick up at 35.475 hours. Forcompleteness sake here is the IVP with this information inserted


Modeling

Q1(t) = 4000− 3998e−3t800

Now,

we need to find tm. We need to do is determine when theamount of pollution reaches 500. So we need to solve.

Q1(t) = 4000− 3998e−3t800 = 500

tm = 35.475



Modeling

Q1(t) = 4000− 3998e−3t800

Now, we need to find tm.

We need to do is determine when theamount of pollution reaches 500. So we need to solve.

Q1(t) = 4000− 3998e−3t800 = 500

tm = 35.475



Modeling

Q1(t) = 4000− 3998e−3t800

Now, we need to find tm. We need to do is determine when theamount of pollution reaches 500.

So we need to solve.

Q1(t) = 4000− 3998e−3t800 = 500

tm = 35.475



Modeling

Q1(t) = 4000− 3998e−3t800


Q1(t) = 4000− 3998e−3t800 = 500

tm = 35.475



Modeling

Q1(t) = 4000− 3998e−3t800


Q1(t) = 4000− 3998e−3t800 = 500

tm = 35.475



Modeling

Q1(t) = 4000− 3998e−3t800


Q1(t) = 4000− 3998e−3t800 = 500

tm = 35.475



Modeling

Q1(t) = 4000− 3998e−3t800


Q1(t) = 4000− 3998e−3t800 = 500

tm = 35.475

So, the second process will pick up at 35.475 hours.

Forcompleteness sake here is the IVP with this information inserted


Modeling

Q1(t) = 4000− 3998e−3t800


Q1(t) = 4000− 3998e−3t800 = 500

tm = 35.475

So, the second process will pick up at 35.475 hours. Forcompleteness sake

here is the IVP with this information inserted


Modeling

Q1(t) = 4000− 3998e−3t800


Q1(t) = 4000− 3998e−3t800 = 500

tm = 35.475



Modeling

Q1(t) = 4000− 3998e−3t800


Q1(t) = 4000− 3998e−3t800 = 500

tm = 35.475



Modeling

Q ′2(t) = −(

2Q2(t)

435.475− t

)Q(35.475) = 50035.475 ≤ t ≤ 435.475

This differential equation is both linear and separable and I willleave the details to you again to check that we should get.

Q2(t) =(435.476− t)2

320


Modeling

Q ′2(t) = −(

2Q2(t)

435.475− t

)Q(35.475) = 50035.475 ≤ t ≤ 435.475

This differential equation is both

linear and separable and I willleave the details to you again to check that we should get.

Q2(t) =(435.476− t)2

320


Modeling

Q ′2(t) = −(

2Q2(t)

435.475− t

)Q(35.475) = 50035.475 ≤ t ≤ 435.475

This differential equation is both linear and separable

and I willleave the details to you again to check that we should get.

Q2(t) =(435.476− t)2

320


Modeling

Q ′2(t) = −(

2Q2(t)

435.475− t

)Q(35.475) = 50035.475 ≤ t ≤ 435.475

This differential equation is both linear and separable and I willleave the details to you again

to check that we should get.

Q2(t) =(435.476− t)2

320


Modeling

Q ′2(t) = −(

2Q2(t)

435.475− t

)Q(35.475) = 50035.475 ≤ t ≤ 435.475


Q2(t) =(435.476− t)2

320


Modeling

Q ′2(t) = −(

2Q2(t)

435.475− t

)Q(35.475) = 50035.475 ≤ t ≤ 435.475


Q2(t) =(435.476− t)2

320


Modeling

Q ′2(t) = −(

2Q2(t)

435.475− t

)Q(35.475) = 50035.475 ≤ t ≤ 435.475


Q2(t) =(435.476− t)2

320


Modeling

So, a solution that encompasses the complete running time of theprocess is

Q(t) =

{4000− 3998e−

3t800 0 ≤ t ≤ 35.475

(435.476−t)2320 35.475 ≤ t ≤ 435.4758


Modeling


Q(t) =

{4000− 3998e−

3t800 0 ≤ t ≤ 35.475

(435.476−t)2320 35.475 ≤ t ≤ 435.4758


Modeling


Q(t) =

{4000− 3998e−

3t800 0 ≤ t ≤ 35.475

(435.476−t)2320 35.475 ≤ t ≤ 435.4758


Modeling

Here is graph of the solution.


Modeling



Modeling



Modeling

Example 16

Escape Velocity

The model of constant gravitation only works when were close tothe surface of the earth, and the distances we’re dealing with aresmall relative to the radius of the earth. If we start to deal withlarger distances, then we must take into account that accelerationfrom gravity is weaker the farther we are away from the earth.Newton’s law of universal gravitation tells us that the force fromgravity experienced a distance r from the center of the earth willbe:

F = −GmM

r2


Modeling

Example 16Escape Velocity


F = −GmM

r2


Modeling


The model of constant gravitation

only works when were close tothe surface of the earth, and the distances we’re dealing with aresmall relative to the radius of the earth. If we start to deal withlarger distances, then we must take into account that accelerationfrom gravity is weaker the farther we are away from the earth.Newton’s law of universal gravitation tells us that the force fromgravity experienced a distance r from the center of the earth willbe:

F = −GmM

r2


Modeling


The model of constant gravitation only works when were close tothe surface of the earth,

and the distances we’re dealing with aresmall relative to the radius of the earth. If we start to deal withlarger distances, then we must take into account that accelerationfrom gravity is weaker the farther we are away from the earth.Newton’s law of universal gravitation tells us that the force fromgravity experienced a distance r from the center of the earth willbe:

F = −GmM

r2


Modeling


The model of constant gravitation only works when were close tothe surface of the earth, and the distances we’re dealing with aresmall relative

to the radius of the earth. If we start to deal withlarger distances, then we must take into account that accelerationfrom gravity is weaker the farther we are away from the earth.Newton’s law of universal gravitation tells us that the force fromgravity experienced a distance r from the center of the earth willbe:

F = −GmM

r2


Modeling


The model of constant gravitation only works when were close tothe surface of the earth, and the distances we’re dealing with aresmall relative to the radius of the earth.

If we start to deal withlarger distances, then we must take into account that accelerationfrom gravity is weaker the farther we are away from the earth.Newton’s law of universal gravitation tells us that the force fromgravity experienced a distance r from the center of the earth willbe:

F = −GmM

r2


Modeling


The model of constant gravitation only works when were close tothe surface of the earth, and the distances we’re dealing with aresmall relative to the radius of the earth. If we start to deal withlarger distances,

then we must take into account that accelerationfrom gravity is weaker the farther we are away from the earth.Newton’s law of universal gravitation tells us that the force fromgravity experienced a distance r from the center of the earth willbe:

F = −GmM

r2


Modeling


The model of constant gravitation only works when were close tothe surface of the earth, and the distances we’re dealing with aresmall relative to the radius of the earth. If we start to deal withlarger distances, then we must take into account that accelerationfrom gravity

is weaker the farther we are away from the earth.Newton’s law of universal gravitation tells us that the force fromgravity experienced a distance r from the center of the earth willbe:

F = −GmM

r2


Modeling


The model of constant gravitation only works when were close tothe surface of the earth, and the distances we’re dealing with aresmall relative to the radius of the earth. If we start to deal withlarger distances, then we must take into account that accelerationfrom gravity is weaker the farther we are away from the earth.

Newton’s law of universal gravitation tells us that the force fromgravity experienced a distance r from the center of the earth willbe:

F = −GmM

r2


Modeling


The model of constant gravitation only works when were close tothe surface of the earth, and the distances we’re dealing with aresmall relative to the radius of the earth. If we start to deal withlarger distances, then we must take into account that accelerationfrom gravity is weaker the farther we are away from the earth.Newton’s law of universal gravitation

tells us that the force fromgravity experienced a distance r from the center of the earth willbe:

F = −GmM

r2


Modeling


The model of constant gravitation only works when were close tothe surface of the earth, and the distances we’re dealing with aresmall relative to the radius of the earth. If we start to deal withlarger distances, then we must take into account that accelerationfrom gravity is weaker the farther we are away from the earth.Newton’s law of universal gravitation tells us that the force fromgravity experienced a distance r

from the center of the earth willbe:

F = −GmM

r2


Modeling



F = −GmM

r2


Modeling



F = −GmM

r2


Modeling



F = −GmM

r2


Modeling

where m is the mass of the object,

M is the mass of the earth, andG is Newtons gravitational constant G = 6.6710−11Nm2/kg2. Wecan use this relation to calculate an objects escape velocity onthe surface of the earth. This is the speed at which an object mustbe moving away from the earth at the earths surface if it is tobreak free from the gravitational attraction of the earth andcontinue to move away forever.

Well, we note that if we move away from the earth along a line thatgoes through the earths center, then Newtons second law tells us:

md2r

dt2= −GmM

r2


Modeling

where m is the mass of the object, M is the mass of the earth,

andG is Newtons gravitational constant G = 6.6710−11Nm2/kg2. Wecan use this relation to calculate an objects escape velocity onthe surface of the earth. This is the speed at which an object mustbe moving away from the earth at the earths surface if it is tobreak free from the gravitational attraction of the earth andcontinue to move away forever.


md2r

dt2= −GmM

r2


Modeling

where m is the mass of the object, M is the mass of the earth, andG is Newtons gravitational constant G = 6.6710−11Nm2/kg2.

Wecan use this relation to calculate an objects escape velocity onthe surface of the earth. This is the speed at which an object mustbe moving away from the earth at the earths surface if it is tobreak free from the gravitational attraction of the earth andcontinue to move away forever.


md2r

dt2= −GmM

r2


Modeling

where m is the mass of the object, M is the mass of the earth, andG is Newtons gravitational constant G = 6.6710−11Nm2/kg2. Wecan use this relation to calculate an objects escape velocity onthe surface of the earth.

This is the speed at which an object mustbe moving away from the earth at the earths surface if it is tobreak free from the gravitational attraction of the earth andcontinue to move away forever.


md2r

dt2= −GmM

r2


Modeling

where m is the mass of the object, M is the mass of the earth, andG is Newtons gravitational constant G = 6.6710−11Nm2/kg2. Wecan use this relation to calculate an objects escape velocity onthe surface of the earth. This is the speed

at which an object mustbe moving away from the earth at the earths surface if it is tobreak free from the gravitational attraction of the earth andcontinue to move away forever.


md2r

dt2= −GmM

r2


Modeling

where m is the mass of the object, M is the mass of the earth, andG is Newtons gravitational constant G = 6.6710−11Nm2/kg2. Wecan use this relation to calculate an objects escape velocity onthe surface of the earth. This is the speed at which an object mustbe moving away from the earth at the earths surface

if it is tobreak free from the gravitational attraction of the earth andcontinue to move away forever.


md2r

dt2= −GmM

r2


Modeling

where m is the mass of the object, M is the mass of the earth, andG is Newtons gravitational constant G = 6.6710−11Nm2/kg2. Wecan use this relation to calculate an objects escape velocity onthe surface of the earth. This is the speed at which an object mustbe moving away from the earth at the earths surface if it is tobreak free from the gravitational attraction of the earth

andcontinue to move away forever.


md2r

dt2= −GmM

r2


Modeling

where m is the mass of the object, M is the mass of the earth, andG is Newtons gravitational constant G = 6.6710−11Nm2/kg2. Wecan use this relation to calculate an objects escape velocity onthe surface of the earth. This is the speed at which an object mustbe moving away from the earth at the earths surface if it is tobreak free from the gravitational attraction of the earth andcontinue to move away forever.


md2r

dt2= −GmM

r2


Modeling


Well,

we note that if we move away from the earth along a line thatgoes through the earths center, then Newtons second law tells us:

md2r

dt2= −GmM

r2


Modeling


Well, we note that if we move away from the earth

along a line thatgoes through the earths center, then Newtons second law tells us:

md2r

dt2= −GmM

r2


Modeling


Well, we note that if we move away from the earth along a line thatgoes through the earths center,

then Newtons second law tells us:

md2r

dt2= −GmM

r2


Modeling



md2r

dt2= −GmM

r2


Modeling



md2r

dt2= −GmM

r2


Modeling



md2r

dt2= −GmM

r2


Modeling

By the chain rule we have

dvdt = dv

drdrdt , and if we note v = dr

dt then we can transform thisrelation into

mvdv

dr= −GmM

r2

If we integrate both sides with respect to r we get:

1

2mv2 =

GmM

r+ c

And applying initial conditions, v(R) = v0, we obtain:

v2 = v20 + 2GM

(1

r− 1

R

)


Modeling

By the chain rule we havedvdt = dv



mvdv

dr= −GmM

r2


1

2mv2 =

GmM

r+ c


v2 = v20 + 2GM

(1

r− 1

R

)


Modeling




mvdv

dr= −GmM

r2


1

2mv2 =

GmM

r+ c


v2 = v20 + 2GM

(1

r− 1

R

)


Modeling




mvdv

dr= −GmM

r2


1

2mv2 =

GmM

r+ c


v2 = v20 + 2GM

(1

r− 1

R

)


Modeling




mvdv

dr= −GmM

r2


1

2mv2 =

GmM

r+ c


v2 = v20 + 2GM

(1

r− 1

R

)


Modeling




mvdv

dr= −GmM

r2


1

2mv2 =

GmM

r+ c


v2 = v20 + 2GM

(1

r− 1

R

)


Modeling




mvdv

dr= −GmM

r2


1

2mv2 =

GmM

r+ c


v2 = v20 + 2GM

(1

r− 1

R

)


Modeling




mvdv

dr= −GmM

r2


1

2mv2 =

GmM

r+ c


v2 = v20 + 2GM

(1

r− 1

R

)


Modeling

If the object is to escape from the graviational action of the earth,

then its velocity must always be positive as r →∞. This will bethe case if

v0 ≥√

2GM

R

For the earth the escape velocity is v0 = 11, 180m/s


Modeling

If the object is to escape from the graviational action of the earth,then its velocity must always be positive as r →∞.

This will bethe case if

v0 ≥√

2GM

R



Modeling

If the object is to escape from the graviational action of the earth,then its velocity must always be positive as r →∞. This will bethe case if

v0 ≥√

2GM

R



Modeling


v0 ≥√

2GM

R



Modeling


v0 ≥√

2GM

R



Modeling


v0 ≥√

2GM

R



Modeling

Example 17

Escape Velocity

Suppose that you are stranded -your rocket engine has failed- onan asteroid of diameter 3 miles, with density equal to that of theearth with radius 3960 miles. If you have enough spring in yourlegs to jump 4 feet straight up on earth while wearing your spacesuit, can you blast off from this asteroid using leg power alone ?

Solution

The escape velocity for the Earth is


Modeling



Solution



Modeling


Suppose that you are stranded -your rocket engine has failed- onan asteroid of diameter 3 miles,

with density equal to that of theearth with radius 3960 miles. If you have enough spring in yourlegs to jump 4 feet straight up on earth while wearing your spacesuit, can you blast off from this asteroid using leg power alone ?

Solution



Modeling


Suppose that you are stranded -your rocket engine has failed- onan asteroid of diameter 3 miles, with density equal to that of theearth with radius 3960 miles.

If you have enough spring in yourlegs to jump 4 feet straight up on earth while wearing your spacesuit, can you blast off from this asteroid using leg power alone ?

Solution



Modeling


Suppose that you are stranded -your rocket engine has failed- onan asteroid of diameter 3 miles, with density equal to that of theearth with radius 3960 miles. If you have enough spring in yourlegs to jump 4 feet straight up on earth

while wearing your spacesuit, can you blast off from this asteroid using leg power alone ?

Solution



Modeling


Suppose that you are stranded -your rocket engine has failed- onan asteroid of diameter 3 miles, with density equal to that of theearth with radius 3960 miles. If you have enough spring in yourlegs to jump 4 feet straight up on earth while wearing your spacesuit,

can you blast off from this asteroid using leg power alone ?

Solution



Modeling


Suppose that you are stranded -your rocket engine has failed- onan asteroid of diameter 3 miles, with density equal to that of theearth with radius 3960 miles. If you have enough spring in yourlegs to jump 4 feet straight up on earth while wearing your spacesuit, can you blast off from this asteroid

using leg power alone ?

Solution



Modeling



Solution



Modeling



Solution



Modeling



Solution



Modeling



Solution



Modeling

vE =

√2GME

RE

Solving for ME in this equation we get:

ME =v2ERE

2G

The density of the earth is its mass divided by its volume

ME43πR

3E

=3v2E

8πGR2E


Modeling

vE =

√2GME

RE


ME =v2ERE

2G


ME43πR

3E

=3v2E

8πGR2E


Modeling

vE =

√2GME

RE


ME =v2ERE

2G


ME43πR

3E

=3v2E

8πGR2E


Modeling

vE =

√2GME

RE


ME =v2ERE

2G


ME43πR

3E

=3v2E

8πGR2E


Modeling

vE =

√2GME

RE


ME =v2ERE

2G


ME43πR

3E

=3v2E

8πGR2E


Modeling

vE =

√2GME

RE


ME =v2ERE

2G


ME43πR

3E

=3v2E

8πGR2E


Modeling

A similar calculation can be done for the asteroid,

and given boththe asteroid and the Earth have the same density we get:

3v2E8πGR2

E

=3v2A

8πGR2A

With a little algebra from this we can deduce the ratio:

v2Av2E

=R2A

R2E

So, the escape velocity from the asteroid is


Modeling

A similar calculation can be done for the asteroid, and given boththe asteroid and the Earth have the same density we get:

3v2E8πGR2

E

=3v2A

8πGR2A


v2Av2E

=R2A

R2E



Modeling


3v2E8πGR2

E

=3v2A

8πGR2A


v2Av2E

=R2A

R2E



Modeling


3v2E8πGR2

E

=3v2A

8πGR2A


v2Av2E

=R2A

R2E



Modeling


3v2E8πGR2

E

=3v2A

8πGR2A


v2Av2E

=R2A

R2E



Modeling


3v2E8πGR2

E

=3v2A

8πGR2A


v2Av2E

=R2A

R2E



Modeling


3v2E8πGR2

E

=3v2A

8πGR2A


v2Av2E

=R2A

R2E



Modeling

vA = vE

(RA

RE

)= 11, 180

(1.5

3960

)= 4.24m/s

At the begining of the jump, all the energy is initially kinetic,12mv2, and at the top of the jump all that energy is converted intopotential energy, mgh. So, the final height is given by the equation:

v =√

2gh

Plugging 4 feet in for h we get:

v =√

2(9.8)(4ft)(1m/3.28ft) = 4.89m/s > 4.24m/s

So, yes, you can get off the asteroid !!!!


Modeling

vA = vE

(RA

RE

)= 11, 180

(1.5

3960

)= 4.24m/s

At the begining of the jump,

all the energy is initially kinetic,12mv2, and at the top of the jump all that energy is converted intopotential energy, mgh. So, the final height is given by the equation:

v =√

2gh


v =√

2(9.8)(4ft)(1m/3.28ft) = 4.89m/s > 4.24m/s



Modeling

vA = vE

(RA

RE

)= 11, 180

(1.5

3960

)= 4.24m/s

At the begining of the jump, all the energy is initially kinetic,12mv2,

and at the top of the jump all that energy is converted intopotential energy, mgh. So, the final height is given by the equation:

v =√

2gh


v =√

2(9.8)(4ft)(1m/3.28ft) = 4.89m/s > 4.24m/s



Modeling

vA = vE

(RA

RE

)= 11, 180

(1.5

3960

)= 4.24m/s

At the begining of the jump, all the energy is initially kinetic,12mv2, and at the top of the jump all that energy

is converted intopotential energy, mgh. So, the final height is given by the equation:

v =√

2gh


v =√

2(9.8)(4ft)(1m/3.28ft) = 4.89m/s > 4.24m/s



Modeling

vA = vE

(RA

RE

)= 11, 180

(1.5

3960

)= 4.24m/s

At the begining of the jump, all the energy is initially kinetic,12mv2, and at the top of the jump all that energy is converted intopotential energy, mgh.

So, the final height is given by the equation:

v =√

2gh


v =√

2(9.8)(4ft)(1m/3.28ft) = 4.89m/s > 4.24m/s



Modeling

vA = vE

(RA

RE

)= 11, 180

(1.5

3960

)= 4.24m/s


v =√

2gh


v =√

2(9.8)(4ft)(1m/3.28ft) = 4.89m/s > 4.24m/s



Modeling

vA = vE

(RA

RE

)= 11, 180

(1.5

3960

)= 4.24m/s


v =√

2gh


v =√

2(9.8)(4ft)(1m/3.28ft) = 4.89m/s > 4.24m/s



Modeling

vA = vE

(RA

RE

)= 11, 180

(1.5

3960

)= 4.24m/s


v =√

2gh


v =√

2(9.8)(4ft)(1m/3.28ft) = 4.89m/s > 4.24m/s



Modeling

vA = vE

(RA

RE

)= 11, 180

(1.5

3960

)= 4.24m/s


v =√

2gh


v =√

2(9.8)(4ft)(1m/3.28ft) = 4.89m/s > 4.24m/s



Modeling

vA = vE

(RA

RE

)= 11, 180

(1.5

3960

)= 4.24m/s


v =√

2gh


v =√

2(9.8)(4ft)(1m/3.28ft) = 4.89m/s > 4.24m/s



Modeling

vA = vE

(RA

RE

)= 11, 180

(1.5

3960

)= 4.24m/s


v =√

2gh


v =√

2(9.8)(4ft)(1m/3.28ft) = 4.89m/s > 4.24m/s



Modeling

Example 18

Compound Interest

Let S be an initial sum of money. Let r represent an interest rate.We can model the growth of an initial deposit with respect to theinterest rate r with differential equations. Let’s assume that theinitial deposit is compounded continuously. If t represents time,then the rate of change of the initial deposit is dS

dt , this quantity isequal to the rate at which interest accrues, which is the interestrate r times the current value of the investment S(t). Thus, themodel is given by

dS

dt= rS(t)


Modeling

Example 18Compound Interest



dS

dt= rS(t)


Modeling


Let S be an initial sum of money.

Let r represent an interest rate.We can model the growth of an initial deposit with respect to theinterest rate r with differential equations. Let’s assume that theinitial deposit is compounded continuously. If t represents time,then the rate of change of the initial deposit is dS


dS

dt= rS(t)


Modeling


Let S be an initial sum of money. Let r represent an interest rate.

We can model the growth of an initial deposit with respect to theinterest rate r with differential equations. Let’s assume that theinitial deposit is compounded continuously. If t represents time,then the rate of change of the initial deposit is dS


dS

dt= rS(t)


Modeling


Let S be an initial sum of money. Let r represent an interest rate.We can model the growth of an initial deposit with respect to theinterest rate r with differential equations.

Let’s assume that theinitial deposit is compounded continuously. If t represents time,then the rate of change of the initial deposit is dS


dS

dt= rS(t)


Modeling


Let S be an initial sum of money. Let r represent an interest rate.We can model the growth of an initial deposit with respect to theinterest rate r with differential equations. Let’s assume that theinitial deposit is compounded continuously.

If t represents time,then the rate of change of the initial deposit is dS


dS

dt= rS(t)


Modeling


Let S be an initial sum of money. Let r represent an interest rate.We can model the growth of an initial deposit with respect to theinterest rate r with differential equations. Let’s assume that theinitial deposit is compounded continuously. If t represents time,

then the rate of change of the initial deposit is dSdt , this quantity is

equal to the rate at which interest accrues, which is the interestrate r times the current value of the investment S(t). Thus, themodel is given by

dS

dt= rS(t)


Modeling



dt ,

this quantity isequal to the rate at which interest accrues, which is the interestrate r times the current value of the investment S(t). Thus, themodel is given by

dS

dt= rS(t)


Modeling



dt , this quantity isequal to the rate at which interest accrues,

which is the interestrate r times the current value of the investment S(t). Thus, themodel is given by

dS

dt= rS(t)


Modeling



dt , this quantity isequal to the rate at which interest accrues, which is the interestrate r times

the current value of the investment S(t). Thus, themodel is given by

dS

dt= rS(t)


Modeling



dt , this quantity isequal to the rate at which interest accrues, which is the interestrate r times the current value of the investment S(t).

Thus, themodel is given by

dS

dt= rS(t)


Modeling




dS

dt= rS(t)


Modeling




dS

dt= rS(t)


Modeling




dS

dt= rS(t)


Modeling

Suppose

that we also know the value of the investment at someparticular time, say,

S(0) = S0

Integrating this separable IVP

dS

dt= rS(t)

1

SdS = rdt∫

1

SdS =

∫rdt

ln|S | = rt + K


Modeling

Suppose that we also know the value of the investment

at someparticular time, say,

S(0) = S0


dS

dt= rS(t)

1

SdS = rdt∫

1

SdS =

∫rdt

ln|S | = rt + K


Modeling

Suppose that we also know the value of the investment at someparticular time, say,

S(0) = S0


dS

dt= rS(t)

1

SdS = rdt∫

1

SdS =

∫rdt

ln|S | = rt + K


Modeling


S(0) = S0


dS

dt= rS(t)

1

SdS = rdt∫

1

SdS =

∫rdt

ln|S | = rt + K


Modeling


S(0) = S0


dS

dt= rS(t)

1

SdS = rdt∫

1

SdS =

∫rdt

ln|S | = rt + K


Modeling


S(0) = S0


dS

dt= rS(t)

1

SdS = rdt∫

1

SdS =

∫rdt

ln|S | = rt + K


Modeling


S(0) = S0


dS

dt= rS(t)

1

SdS = rdt∫

1

SdS =

∫rdt

ln|S | = rt + K


Modeling


S(0) = S0


dS

dt= rS(t)

1

SdS = rdt

∫1

SdS =

∫rdt

ln|S | = rt + K


Modeling


S(0) = S0


dS

dt= rS(t)

1

SdS = rdt∫

1

SdS =

∫rdt

ln|S | = rt + K


Modeling


S(0) = S0


dS

dt= rS(t)

1

SdS = rdt∫

1

SdS =

∫rdt

ln|S | = rt + K


Modeling


S(0) = S0


dS

dt= rS(t)

1

SdS = rdt∫

1

SdS =

∫rdt

ln|S | = rt + K


Modeling

S(t) = cert

and using the initial condition that S(0) = S0, we have that theconstant of integration is c = S0. Therefore the solution to thisinitial value problem is:

S(t) = S0ert


Modeling

S(t) = cert

and using the initial condition that S(0) = S0,

we have that theconstant of integration is c = S0. Therefore the solution to thisinitial value problem is:

S(t) = S0ert


Modeling

S(t) = cert

and using the initial condition that S(0) = S0, we have that theconstant of integration is c = S0.

Therefore the solution to thisinitial value problem is:

S(t) = S0ert


Modeling

S(t) = cert


S(t) = S0ert


Modeling

S(t) = cert


S(t) = S0ert


Modeling

S(t) = cert


S(t) = S0ert


Modeling

Example 19

Compound Interest

Let S be an initial sum of money. Let r represent an interest rate.Assume that the initial deposit is compounded continuously. Let’suppose that there may be deposits or withdrawals in addition tothe accrual of interest, dividends, or capital gains and the depositsor withdrawals take place at a constant rate k. So the IVP is

dS

dt= rS(t) + k S(0) = S0

( k > 0 for deposits and k < 0 for withdrawals)


Modeling



dS

dt= rS(t) + k S(0) = S0



Modeling


Let S be an initial sum of money.

Let r represent an interest rate.Assume that the initial deposit is compounded continuously. Let’suppose that there may be deposits or withdrawals in addition tothe accrual of interest, dividends, or capital gains and the depositsor withdrawals take place at a constant rate k. So the IVP is

dS

dt= rS(t) + k S(0) = S0



Modeling


Let S be an initial sum of money. Let r represent an interest rate.

Assume that the initial deposit is compounded continuously. Let’suppose that there may be deposits or withdrawals in addition tothe accrual of interest, dividends, or capital gains and the depositsor withdrawals take place at a constant rate k. So the IVP is

dS

dt= rS(t) + k S(0) = S0



Modeling


Let S be an initial sum of money. Let r represent an interest rate.Assume that the initial deposit is compounded continuously.

Let’suppose that there may be deposits or withdrawals in addition tothe accrual of interest, dividends, or capital gains and the depositsor withdrawals take place at a constant rate k. So the IVP is

dS

dt= rS(t) + k S(0) = S0



Modeling


Let S be an initial sum of money. Let r represent an interest rate.Assume that the initial deposit is compounded continuously. Let’suppose that there may be deposits or withdrawals in addition tothe accrual of interest,

dividends, or capital gains and the depositsor withdrawals take place at a constant rate k. So the IVP is

dS

dt= rS(t) + k S(0) = S0



Modeling


Let S be an initial sum of money. Let r represent an interest rate.Assume that the initial deposit is compounded continuously. Let’suppose that there may be deposits or withdrawals in addition tothe accrual of interest, dividends, or capital gains and the depositsor withdrawals take place at a constant rate k.

So the IVP is

dS

dt= rS(t) + k S(0) = S0



Modeling



dS

dt= rS(t) + k S(0) = S0



Modeling



dS

dt= rS(t) + k S(0) = S0



Modeling



dS

dt= rS(t) + k S(0) = S0



Modeling



dS

dt= rS(t) + k S(0) = S0



Modeling

The above differential equation is a linear one,

with integratingfactor e−rt , so its general solution is:

S(t) = cert − k

r

and using the initial condition that S(0) = S0, we have that theconstant of integration is c = S0 + k

r . Therefore the solution tothis initial value problem is:

S(t) = S0ert +

k

r

(ert − 1

)


Modeling

The above differential equation is a linear one, with integratingfactor e−rt ,

so its general solution is:

S(t) = cert − k

r



S(t) = S0ert +

k

r

(ert − 1

)


Modeling

The above differential equation is a linear one, with integratingfactor e−rt , so its general solution is:

S(t) = cert − k

r



S(t) = S0ert +

k

r

(ert − 1

)


Modeling


S(t) = cert − k

r



S(t) = S0ert +

k

r

(ert − 1

)


Modeling


S(t) = cert − k

r

and using the initial condition that S(0) = S0,

we have that theconstant of integration is c = S0 + k


S(t) = S0ert +

k

r

(ert − 1

)


Modeling


S(t) = cert − k

r


r .

Therefore the solution tothis initial value problem is:

S(t) = S0ert +

k

r

(ert − 1

)


Modeling


S(t) = cert − k

r



S(t) = S0ert +

k

r

(ert − 1

)


Modeling


S(t) = cert − k

r



S(t) = S0ert +

k

r

(ert − 1

)


Modeling


S(t) = cert − k

r



S(t) = S0ert +

k

r

(ert − 1

)


Modeling

Example 20

Newton’s Law of Cooling

Newton’s Law of Cooling states that the temperature of a bodychanges at a rate proportional to the difference in temperaturebetween its own temperature and the temperature of itssurroundings.

We can therefore write

dT

dt= −k (T − Ts)


Modeling

Example 20Newton’s Law of Cooling



dT

dt= −k (T − Ts)


Modeling


Newton’s Law of Cooling states

that the temperature of a bodychanges at a rate proportional to the difference in temperaturebetween its own temperature and the temperature of itssurroundings.


dT

dt= −k (T − Ts)


Modeling


Newton’s Law of Cooling states that the temperature of a body

changes at a rate proportional to the difference in temperaturebetween its own temperature and the temperature of itssurroundings.


dT

dt= −k (T − Ts)


Modeling


Newton’s Law of Cooling states that the temperature of a bodychanges at a rate proportional to the difference in temperature

between its own temperature and the temperature of itssurroundings.


dT

dt= −k (T − Ts)


Modeling


Newton’s Law of Cooling states that the temperature of a bodychanges at a rate proportional to the difference in temperaturebetween its own temperature

and the temperature of itssurroundings.


dT

dt= −k (T − Ts)


Modeling




dT

dt= −k (T − Ts)


Modeling




dT

dt= −k (T − Ts)


Modeling




dT

dt= −k (T − Ts)


Modeling




dT

dt= −k (T − Ts)


Modeling

where,

T = Temperature of the body at any time tTs= Temperature of the surroundings (also called ambienttemperature)T0 = Initial temperature of the bodyk = constant of proportionality

Integrating this separable differential equation

dT

dt= −k (T − Ts)


Modeling

where,

T = Temperature of the body at any time t

Ts= Temperature of the surroundings (also called ambienttemperature)T0 = Initial temperature of the bodyk = constant of proportionality


dT

dt= −k (T − Ts)


Modeling

where,

T = Temperature of the body at any time tTs= Temperature of the surroundings (also called ambienttemperature)

T0 = Initial temperature of the bodyk = constant of proportionality


dT

dt= −k (T − Ts)


Modeling

where,

T = Temperature of the body at any time tTs= Temperature of the surroundings (also called ambienttemperature)T0 = Initial temperature of the body

k = constant of proportionality


dT

dt= −k (T − Ts)


Modeling

where,



dT

dt= −k (T − Ts)


Modeling

where,



dT

dt= −k (T − Ts)


Modeling

where,



dT

dt= −k (T − Ts)


Modeling

where,



dT

dt= −k (T − Ts)


Modeling

1

T − TsdT = −kdt

∫1

T − TsdT = −

∫kdt

ln|T − Ts | = −kt + C

|T − Ts | = e−kt+C


Modeling

1

T − TsdT = −kdt∫

1

T − TsdT = −

∫kdt

ln|T − Ts | = −kt + C

|T − Ts | = e−kt+C


Modeling

1


1

T − TsdT = −

∫kdt

ln|T − Ts | = −kt + C

|T − Ts | = e−kt+C


Modeling

1


1

T − TsdT = −

∫kdt

ln|T − Ts | = −kt + C

|T − Ts | = e−kt+C


Modeling

1


1

T − TsdT = −

∫kdt

ln|T − Ts | = −kt + C

|T − Ts | = e−kt+C


Modeling

T = Ts + ce−kt ; T > Ts (why?)

Applying initial conditions T (0) = T0

c = T0 − Ts

Thus, the solution is

T = Ts + (T0 − Ts)e−kt


Modeling



c = T0 − Ts




Modeling



c = T0 − Ts




Modeling



c = T0 − Ts




Modeling



c = T0 − Ts




Modeling



c = T0 − Ts




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Ordinary Di erential Equations. Session 2roquesol/Math_308_Fall_2017... · 2017-09-12 · Linear and Nonlinear Equations Theorem 1 (Existence and Uniqueness). Suppose p(t) and g(t)