1. What Is the Momentum of a 2500 Kg Car Moving Westward at 15 M/S?

Momentum Unit Assignment

1. What is the momentum of a 2500 kg car moving westward at 15 m/s?

2. A vehicle possesses 1000 units of momentum. What is the vehicle’s new momentum if its velocity is doubled and its mass was tripled?

3. A 25 kg object is moving at 15 m/s on a friction free surface. It collides with and attaches itself to a 40 kg object that was initially at rest. With what velocity do the attached objects now travel?

4. A 2 kg object traveling at 20 m/s collides with a 3 kg object that was moving in the opposite direction at - 5 m/s. If the 2 kg object moves away at -7 m/s after the collision, what is the velocity of the 3 kg object after collision?

5. A train traveling at 20 km/hr attaches itself to a rail car that is initially at rest. How fast do the two coast together if the train has 7 times the mass of the rail car?

6. For a constant force, if the duration of impact on an object is tripled, how much is the impulse increased?

7. Distinguish between impulse and momentum. Which is force x time, and which is inertia in motion?

8. Explain why it is a good thing for a driver if the time of impact in a collision lasts longer.

9. Why does more impulse happen during a collision when bouncing occurs than during a collision when it doesn’t? (recall that impulse = ∆momentum, and that momentum is a vector quantity)

10. For any closed system, what does it mean to say that the system’s momentum is conserved?

11. What is the difference between an elastic and inelastic collision?

12. A force of 940 N acts on a bicycle for 8.5 seconds.

a) what is the impulse on the bicycle? (leave answer with proper units)

b) what change in momentum occurs on the bicycle? (use proper units)

c) what is the final speed of the bicycle if the mass of the bicycle is 77 kg and is initially at rest? (use proper units, and leave to one decimal place)

13. What two things does a change in an object’s momentum depend on?

(ie. What two things does a mass in motion rely on to actually be a mass in motion?)

Solutions

1. What is the momentum of a 2500 kg car moving westward at 15 m/s?

p = mv

p = (2500 kg)(15 m/s) = 37 500 kg*m/s, west

2. A vehicle possesses 1000 units of momentum. What is the vehicle’s new momentum if its velocity is doubled and its mass was tripled?

6000 units

mvbefore = mv after

mvbefore = (25 kg)(15 m/s) = 375 units of momentum

mv after = 25v + 40v

So, 375 = 25v + 40v

375 = 65v

v = 5.8 m/s

mv before = mv after

(m1v1) + (m2v2) = (m1v1) + (m2v2)

(2 kg)(20 m/s) + (3 kg)(-5 m/s) = (2 kg)(-7 m/s) + (3 kg)(v)

40 – 15 = -14 + 3v

39 = 3v

v = 13 m/s

5. A train traveling at 20 km/hr attaches itself to a rail car that is initially at rest. How fast do the two coast together if the train has 7 times the mass of the rail car?

mv before = mv after

(7m)(20) = (7m + m)(v)

140m = (8m)(v)

v = 17.5 km/hr

6. For a constant force, if the duration of impact on an object is tripled, how much is the impulse increased?

Also tripled

7. Distinguish between impulse and momentum. Which is force x time, and which is inertia in motion?

Impulse is force x time, and momentum is inertia in motion.

8. Explain why it is a good thing for a driver if the time of impact in a collision lasts longer.

Greater time means less force

9. Why does more impulse happen during a collision when bouncing occurs than during a collision when it doesn’t? (recall that impulse = ∆momentum, and that momentum is a vector quantity)

The change in momentum (∆mv) is greater so the impulse is greater. The difference between the velocities before and after the bounce is greatest because the velocity before the bounce is positive while the velocity after the bounce is negative (vectors)

10. For any closed system, what does it mean to say that the system’s momentum is conserved?

The momentum before and after an event is the same.

11. What is the difference between an elastic and inelastic collision?

Elastic = bouncing occurs

Inelastic = attach together and generate heat

12. A force of 940 N acts on a bicycle for 8.5 seconds.

a) what is the impulse on the bicycle? (leave answer with proper units)

impulse = ft = (940)(8.5) = 7990 N*s

b) what change in momentum occurs on the bicycle? (use proper units)

since ft = ∆mv, we have 7990 kg*m/s

c) what is the final speed of the bicycle if the mass of the bicycle is 77 kg and is initially at rest? (use proper units)

ft = mv, v = ft/m = 7990/77 = 103.7 m/s

13. What two things does a change in an object’s momentum depend on?

(ie. What two things does a mass in motion rely on to actually be a mass in motion?)

-the amount of force that acts

-length of time that the force acts