Unit 9 Review

Conceptual Physics Unit 9: Momentum Review

Please answer these in your notebook; do not turn this in.

In addition to the questions below, you will need to be able to calculate momentum, change in momentum, impulse, force of impact, and time of impact, just like on the ranking task worksheets we completed.

1. If the time of impact in a collision is extended by four times, how does the force of impact change?

2. When you throw a ball, do you experience an impulse? What if you instead catch a ball of the same speed? What if you catch it, then throw it out again? Which impulse is greatest? (Visualize yourself on a skateboard.)

3. In terms of momentum conservation, why does a gun kick (recoil) when fired?

4. Imagine that you are hovering next to a space shuttle in orbit around the earth and your buddy of equal mass who is moving at 4 m/s with respect to the ship bumps into you. If he holds onto you, how fast do you both move with respect to the ship?

5. Everybody knows that you will be harmed less if you fall on a floor with “give” (like a firemen’s net) than a hard floor. In terms of impulse and momentum, why is this so?

6. If you throw a heavy rock from your hands while standing on a skateboard, you roll backwards. Would you roll backwards if you didn’t actually throw the rock, but went through the motions of doing so? Explain.

7. A bug and the windshield of a fast-moving car collide. Tell whether the following statements are true or false:
1. The forces of impact on the bug and on the car are the same size.
2. The impulses on the bug and on the car are the same size.
3. The changes of speed (acceleration) of the bug and of the car are the same.
4. The changes in momentum of the bug and of the car are the same size.

8. Who is in greater trouble – a person who comes to an abrupt stop when he falls to the pavement or a person that bounces from the same pavement on impact? Explain.

9. A railroad diesel engine has 4 times the mass of a flatcar. If a diesel engine coasts at 5 m/s into a flatcar that is initially at rest, how fast do the two coast after they hook together?

10. If a skater who is spinning pulls her arms in so as to reduce her moment of inertia to half of what it was, how will her rotational speed change? Explain.

11. You sit in the middle of a large, freely rotating turntable at an amusement park. If you crawl toward the outer rim, does the rotational velocity increase, decrease, or remain the same? Explain.