CONSERVATION OF MOMENTUM KEY
Instructions: Show your work completely in your journal when answering the following questions.
1. A billiard ball (mass = 0.15 kg) is moving at 1.0 ⁄ . It rebounds from a side cushion with
the same speed.
a. What was the ball's change in momentum? (Note: Be sure to designate which
direction is "positive" and "negative.")
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b. How is momentum conserved in this collision?
The momentum is conserved in the system. Since the ball collides
with the side cushion, when we consider the cushion we will see
momentum is conserved.
2. A 4.0 kg mass is moving at 3.0 ⁄ toward the right and a 6.0 kg mass is moving at 2.0 ⁄
to the left on a horizontal frictionless table. If the two masses collide and remain together
after the collision, what is their final momentum?
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3. A toy train car with a mass of 200. g and a velocity of 0.80 ⁄ collides with a second car
that is at rest and has equal mass. The two cars couple together.
a. Assuming no friction, what is the velocity of the 2 cars after collision?
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b. What is the momentum of the 2-car system before and after the collision?
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c. The two moving cars above collide with a 3rd car, mass of 150 g (at rest), and couple
together. What is the resulting velocity of the 3 cars?
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d. What is the momentum before and after the collision?
4. A small child on a sled (total mass 45 kg) is pulled so that the sled goes from rest to 4.5
m/s.
a. If the force applied is 40. N, what is the total distance covered during the impulse?
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b. What is the change in momentum of the child and sled? Is momentum conserved?
Explain…
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When we only look at the child on the sled, there is a change in momentum.
However, momentum is conserved for the whole system.
5. A 1200 kg railroad car travels alone on a level frictionless track with a constant speed of 18
⁄ . A 5750 kg additional load (initially at rest) is dropped onto the car. What will the cars
speed be after the additional cargo is added?
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6. A 9500 kg boxcar traveling at 16 ⁄ strikes a second car at rest. The two stick together
and move off with a speed of 6.0 ⁄ . What is the mass of the second car?
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