ObjectiveObjective: : MCAS MCAS review- Speed and review- Speed and

AccelerationAcceleration

Homework: Finish Homework: Finish questionsquestions

Do Now:Do Now:

• Answer in notes:Answer in notes:

Look up the equation for Look up the equation for average average accelerationacceleration and write it down. and write it down.

• A car has an oil drip. A car has an oil drip. As the car moves, it As the car moves, it drips oil at a regular drips oil at a regular rate, leaving a trail rate, leaving a trail of spots on the road.of spots on the road.

Which of the following Which of the following diagrams of the car’s diagrams of the car’s trail of spots shows trail of spots shows the car continuously the car continuously slowing down?slowing down?

•   A. B. C. D.A. B. C. D.

Slowing down = speed (or velocity)

What variable and equation for velocity?Velocity = v

v =∆x/∆t So to slow down, would need less distance over time

How to cheat using the How to cheat using the formula sheetformula sheet

1.1. Find what the question is Find what the question is asking for (underline)asking for (underline)

2.2. Look up what’s underlined Look up what’s underlined and find variable for itand find variable for it

3.3. Find equation that is for Find equation that is for that variablethat variable

4.4. Read equation like Read equation like sentence (may need to look sentence (may need to look up what other variables up what other variables man in the equation)man in the equation)

5.5. Answer or solve the Answer or solve the problemproblem

(if problem, use 4 steps for (if problem, use 4 steps for problem solving)problem solving)

Ex: “What is Ex: “What is work?”work?”

Ex: W = WorkEx: W = Work

Ex: W = FdEx: W = Fd

Ex:Ex: Work is Work is force force multiplied multiplied by distanceby distance

How far did the car How far did the car move during the first move during the first 15 s of the trip?15 s of the trip?

  A.20 m A.20 m B.25 mB.25 m  C.300 m C.300 m D.500 mD.500 m

How far? Asking for…Distance or displacementDistance = d,

displacement = x

No equation for distanceWhat have we can work with?

Know velocity (v) and time (t)Use equation:

Average velocity = ∆x/∆t

Use triangle to solve for ∆x

x

∆v

∆t

∆t

∆x= ∆v∆t

Get numbers from graph

∆x = 20 x 15 = 300m

The graph below illustrates the The graph below illustrates the position and time for a dog that position and time for a dog that runs to catch a stick and then runs to catch a stick and then returns with it.returns with it.

The dog caught the stick after 2 The dog caught the stick after 2 s. What was the dog’s average s. What was the dog’s average speed as he returned with the speed as he returned with the stick?stick?

  A.His average return speed was A.His average return speed was 0.7 m/s.0.7 m/s.

  B.His average return speed was B.His average return speed was 0.9 m/s. 0.9 m/s. 

C.His average return speed was 2 C.His average return speed was 2 m/s. m/s. 

D.His average return speed was 4 D.His average return speed was 4 m/s.m/s.

Average speed = d/∆t

Now need to put in what known to solve equation. Get what known from graph

Need data only for return part of trip.

Remember return means line goes down (goes closer to home)

d = 7-0 = 7m t =10-

2= 8s

Average speed = d/∆t

Average speed= 7/8 = .87

=.9m/s

Two soccer players, X and Y, are kicking a ball back and forth to each other, as shown below. A soccer player is kicking a soccer ball to another player.The table below shows the distance and direction the ball moves after each of four kicks.

Kick Player Distance and Direction1 X 5 m right2 Y 4 m left3 X 6 m right4 Y 5 m left

What is the total displacement of the ball and the total distance traveled by the ball?

A. The ball has a displacement of 2 m to the right and traveled a distance of 20 m. B. The ball has a displacement of 20 m to the right and traveled a distance of 2 m. C. The ball has a displacement of 9 m to the right and traveled a distance of 11 m. D. The ball has a displacement of 11 m to the right and traveled a distance of 9 m.

Distance how far in any direction; displacement how far from where started!

Distance= 5 + 4 + 6 + 5 = 20m

Displacement= 5 - 4 + 6 - 5 = 2m

Try this on your own! Use Try this on your own! Use the problem solving steps the problem solving steps and the formula sheet.and the formula sheet.

How long will it take a car to How long will it take a car to accelerateacceleratefrom 20 m/s to 26 m/s at a rate offrom 20 m/s to 26 m/s at a rate of1.4 m/s2?1.4 m/s2?

  A.2.2 s A.2.2 s 

B.2.7 s B.2.7 s 

C.4.3 s C.4.3 s 

D.4.6 sD.4.6 s

How long: time = tWe have Vi and Vf and acceleration.

What equation has those and t in it?

Average Accelration = ∆V/∆t

Need to solve for t, so have to rearrange equation

a

∆v

∆t

∆t = ∆v/a∆t = 26-20/1.4∆t = 6/1.4= 4.3s

The graph below relates velocity The graph below relates velocity to time.to time.

The graph would The graph would most likelymost likely apply toapply towhich of the following events?which of the following events?

  A.A soccer ball that is at rest A.A soccer ball that is at rest isissuddenly kicked. suddenly kicked. 

B.A ball is thrown upward and B.A ball is thrown upward and returnsreturnsto the ground. to the ground. 

C.A person who is running at aC.A person who is running at aconstant speed decides to run constant speed decides to run faster. faster. 

D.A car traveling at a constant D.A car traveling at a constant speedspeedapplies its brakes and comes to applies its brakes and comes to a stop.a stop.

Flat line= constant velocity

Line down= velocity decreases

v = 0

Write in notesWrite in notes

What is the What is the difference between between speedspeed and and velocityvelocity??