Fall Final ReviewWKS: WORD PROBLEMS

Part II

1. A car travels at a constant speed of 15 m/s for 10 seconds. How far did it go?

1. A car travels at a constant speed of 15 m/s for 10 seconds. How far did it go?

t

dv

t

dv vtd rearrange

ssmd 10/15

md 150

2. How much time will it take to walk 100 meters at a constant speed of 2 m/s?

2. How much time will it take to walk 100 meters at a constant speed of 2 m/s?

t

dv

t

dv

v

dt rearrange

sm

mt

/2

100 st 50

3. You drop an object off the top of a 75 meter tall building. It falls freely and hits the ground 7 seconds later. What is the average speed of the object as it fell?

3. You drop an object off the top of a 75 meter tall building. It falls freely and hits the ground 7 seconds later. What is the average speed of the object as it fell?

t

dv

s

mv

7

75

smv /7.10

4. You drop a rock off the top of a tall cliff. How fast is it traveling 3 seconds later?

4. You drop a rock off the top of a tall cliff. How fast is it traveling 3 seconds later?

gtvv 0

You are asked to calculate the final velocity (v)

Initial velocity: V0 = 0 since you “dropped” the rock

sv 3100

smv /30

5. You drop a 4.0 kg rock from a height of 20.0 meters above the ground. How long will it take to hit the ground?

5. You drop a 4.0 kg rock from a height of 20.0 meters above the ground. How long will it take to hit the ground?

g

dt

2

10

202 mt

In a free fall problem the mass does not change the acceleration of an object when there is no air resistance

st 2

4t

6. According to the figure below, what is the acceleration of the block?

6. According to the figure below, what is the acceleration of the block?

m

Fa

First you need to calculate the net force (20 -10 =10)

kg

Na

20

10 2/5.0 sma

7. A net force of 10 Newtons is used to push a car about 25 yds. The car’s acceleration is 1.0 m/s2. What is the mass of the car?

7. A net force of 10 Newtons is used to push a car about 25 yds. The car’s acceleration is 1.0 m/s2. What is the mass of the car?

maF rearrangea

Fm

2/0.1

10

sm

Nm kgm 10

8. You kick a 0.5 kg stationary ball with a force of 20 Newtons. What is the force on your foot?

8. You kick a 0.5 kg stationary ball with a force of 20 Newtons. What is the force on your foot?

Newton’s Third Law states that the forces are equal and opposite in direction

Force would be 20N

9. If you have a weight of -850 Newtons, and are standing on the ground. What is the force that the Earth is pushing back up on you?

9. If you have a weight of -850 Newtons, and are standing on the ground. What is the force that the Earth is pushing back up on you?

850 N

-850 N

Remember that weight (force of gravity) is pointed downward. We can represent down with a (-) sign

10. What happens to the gravitational attraction (the force) between two objects when the distance between them increases? decreases?

10. What happens to the gravitational attraction (the force) between two objects when the distance between them increases? decreases?

221

d

mmGF

Newton’s Law of Universal Gravitation tells us the relationship of distance and mass on the gravitational force

Distance is on the bottom so it is inversely proportional-distance gets greater, force gets smaller

When distance decreases, force increases

11. When an object is moving in uniform circular motion, which way is it accelerating?

11. When an object is moving in uniform circular motion, which way is it accelerating?

Both acceleration and centripetal force are pointed to the center of the circle

12. Each of the 3 objects below moves with a velocity of 1m/s. What is the total kinetic energy of the system?

12. Each of the 3 objects below moves with a velocity of 1m/s. What is the total kinetic energy of the system?

2

2

1mvE

To calculate total kinetic energy you need to add up the masses of the 3 objects.

2/152

1smkgE JE 5.2

13. What is the kinetic energy of an object with a mass of 5 kg traveling at a speed of 10 meters/second? Assume no other forces act upon the object.

13. What is the kinetic energy of an object with a mass of 5 kg traveling at a speed of 10 meters/second? Assume no other forces act upon the object.

2

2

1mvE 2/105

2

1smkgE

JE 250

14. You lift a heavy rock with a mass of 15 kg to a height of 5.0 meters above the ground. What is the potential energy given to the rock?

14. You lift a heavy rock with a mass of 15 kg to a height of 5.0 meters above the ground. What is the potential energy given to the rock?

mghE mkgE 0.51015

JE 750

15. A 1.5 kg rock falls to the ground off the top of a 25 meter tall cliff. What is the Kinetic energy of the rock right before it hits the ground?

15. A 1.5 kg rock falls to the ground off the top of a 25 meter tall cliff. What is the Kinetic energy of the rock right before it hits the ground?

We do not have velocity to use in equation for KE.

Calculate the PE knowing it will all be transformed into KE

mghE mkgE 25105.1

JE 375

16. A 3.5 kg object is moving with a velocity of 2.0 m/s. What is its momentum?

16. A 3.5 kg object is moving with a velocity of 2.0 m/s. What is its momentum?

mvp smkgp /0.25.3

smkgp /0.7

17. The diagram below represents an inelastic collision between two blocks on a frictionless air track. After the collision the two objects “stick” together. What is the mass of the second box?

17. The diagram below represents an inelastic collision between two blocks on a frictionless air track. After the collision the two objects “stick” together. What is the mass of the second box?

Calculate the total momentum of both boxes before the collision. It will have the same total momentum after as well

mvpblock 1 400/20201 smkgpblockmvpblock 2 00?2 blockp

4000400 totalp

17. The diagram below represents an inelastic collision between two blocks on a frictionless air track. After the collision the two objects “stick” together. What is the mass of the second box?

Since the total momentum before = 400

Total momentum after = 400

mvpafter 15400 m kgmtotal 7.2615

400

18. When the two objects of different mass collide and couple together, what will be their resultant velocity?

18. When the two objects of different mass collide and couple together, what will be their resultant velocity?

Calculate the total momentum of both boxes before the collision. It will have the same total momentum after as well

mvpblock 1 1005201 blockp

mvpblock 2 0052 blockp

1000100 totalp

18. When the two objects of different mass collide and couple together, what will be their resultant velocity?

Since the total momentum before = 100

Total momentum after = 100

mvpafter v15100 smv /7.615

100