You are given two carts, A and B. They look identical, and you are told they are made of the same material. You put A at rest on a low-friction

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1 You are given two carts, A and B. They look identical, and you are told they are made of the same material. You put A at rest on a low-friction track, then send B towards it to the right. After the collision, both carts move to the right, the velocity of B being smaller than what it was before the collision. What do you conclude? A. Cart A must be hollow B. Cart B must be hollow C. The carts really are identical D. Need more information 1

2 These plots show the velocities for test collisions between carts A, B, and S. Which cart (or carts) has (have) the largest inertia? A. A B. B C. S D. Need more information 2

3 These plots show the velocities for test collisions between carts A, B, and S. Which cart (or carts) has (have) the largest inertia? A. A B. B C. S D. Need more information 3

4 These plots show the velocities for test collisions between carts A, B, and S. How do the inertias of A and B compare? A. A > B B. A = B C. A < B D. Need more information 4

5 These plots show the velocities for test collisions between carts A, B, and S. How do the inertias of A and B compare? A. A > B B. A = B C. A < B D. Need more information 5

6 Consider the following situations: i. A ball moving at speed v is brought to rest. ii. The same ball is projected from rest so that it moves at speed v. iii. The same ball moving at speed v is brought to rest, then projected backwards at speed v. In which case(s) does the ball experience the largest change in momentum? A. Case i B. Cases i and ii C. Cases i, ii, and iii D. Case ii E. Cases ii and iii F. Case iii 6

7 You are lying in bed and you want to shut your bedroom door. You have a superball and a blob of clay (both with the same mass) sitting next to you. Which one would be more effective to throw at your door to close it? A. the superball B. the blob of clay C. it doesn t matter -- they will be equally effective D. you are just too lazy to throw anything 7

8 A small car and a large truck collide head-on and stick together. Which one has the larger momentum change? A. the car B. the truck C. they both have the same momentum change D. can t tell without knowing the final velocities 8

9 A box slides with initial velocity 10 m/s on a frictionless surface and collides inelastically with an identical box. The boxes stick together after the collision. What is the final velocity? A. 10 m/s B. 20 m/s C. 0 m/s D. 15 m/s E. 5 m/s M M v i M M v f 9

10 An open cart rolls along a frictionless track while it is raining. As it rolls, what happens to the speed of the cart as the rain collects in it? (Assume that the rain falls vertically into the box.) A. speeds up B. maintains constant speed C. slows down D. stops immediately 10

11 Which of these systems is isolated? (A = yes, B = no) 1. While slipping on a patch of ice, a car collides with another car. System = both cars 2. Same as in situation 1. System = slipping car 3. A single car slips on a patch of ice. System = car 4. A car makes an emergency stop on the road. System = car 5. A ball drops to earth. System = ball 6. A billiard ball collides with another ball on a pool table. System = both balls 11

12 Suppose the entire population of Earth were to gather in one spot and jump up at the same time. While all the people are in the air, does Earth gain momentum in the opposite direction? A. No, Earth s inertia is so large that it does not move at all. B. Yes, but because Earth s inertia is so large, its change in momentum is much smaller than that of all the jumping people. C. Yes, Earth recoils just like a rifle firing a bullet, with a change in momentum that is equal and opposite to that of the jumping people. D. It depends. 12

13 A car accelerates from rest. In so doing, the car gains a certain velocity and Earth gains A. a larger velocity. B. a smaller velocity. C. the same velocity. D. In depends on the interaction between the earth and car. 13

14 Can a stationary object be struck by a moving object and have a larger final momentum than the initial momentum of the incoming object? A. Yes B. No; this would violate the law of conservation of momentum. 14

15 Suppose you are on a cart, initially at rest on a track with very low friction. You throw balls off the cart as shown. Does the cart move? A. Yes, it moves to the right. B. Yes, it moves to the left. C. No, it remains in place. 15

16 Suppose you are on a cart, initially at rest on a track with very low friction. You throw balls at a wall that is rigidly mounted to the cart. If the balls bounce straight back as shown, does the cart move? A. Yes, it moves to the right. B. Yes, it moves to the left. C. No, it remains in place. 16