Name: ________________________________

Momentum Transfer ModelNew Fundamental Principle

New Representation: IFF Charts

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Experiment: Cart Crash

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Activity/Notes: N2L, Collisions, and Conservation

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Worksheet 1: IFF Charts in Action

1. An astronaut whose mass is 80 kg carries an empty oxygen tank with a mass of 10 kg. He throws the tank away from himself with a speed of 2 m/s. With what velocity does he start to move off into space?

2. A 2 kg melon is balanced on your bald uncle’s head. His son, Throckmorton, shoots a 50 g arrow at it with a speed of 30 m/s. The arrow passes through the melon and emerges with a speed of 18 m/s. Find the speed of the melon as it flies off the man’s head.

3. A tennis player returns a 30 m/s serve straight back at 25 m/s, after making contact with the ball for 0.5 s. If the ball has a mass of 0.2 kg, what is the force she exerted on the ball?

image from thingsonyourhead.com (no, seriously)

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4. A raft of mass 180 kg carries two swimmers with masses 50 kg and 80 kg.

The raft is initially floating at rest. The two swimmers simultaneously dive off opposite ends of the raft, each with a horizontal velocity of 3 m/s. With what velocity and in what direction does the raft start to move?

5. One way of measuring the muzzle velocity of a bullet is to fire it horizontally into a massive block of wood placed on a cart. Assuming no friction, we then measure the velocity with which the wood containing the bullet and cart begin to move. In one experiment the bullet had a mass of 50 g and the wood and its cart had a combined mass of 10 kg. After the shot, the cart, wood, and bullet moved at a constant speed, traveling 0.80 m in 0.40 s. From this data determine the original speed of the bullet. (That is, the speed of the bullet right before it hits the cart.)

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6. A 50 kg cart is moving across a very low friction floor at 2.0 m/s. A 70 kg boy, riding in the cart, jumps off so that he hits the floor with zero velocity. What is the change in momentum of the cart?

7. A ball of mass 3 kg, moving at 2 m/s eastward, strikes head-on a ball of mass 1 kg that is moving at 2 m/s westward. The balls stick together after the impact. What is the magnitude and direction of the velocity of the combined mass after the collision?

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Worksheet 2: Explaining with MTM

8. If you throw a ball horizontally while standing on roller skates, you roll backwards. Will you roll backwards if you go through the motions of throwing the ball, but hold on to it instead? Explain your reasoning.

9. Which has the greater change in momentum, a 50 gram clay ball that strikes a wall at 1 m/s and sticks or a 50 gram superball that strikes a wall at 1 m/s and bounces away from the wall at 0.8 m/s? Explain your reasoning.

10. Why are padded dashboards safer than hard dashboards in automobiles?

11. Why are nylon ropes, which stretch considerably under stress, favored by mountain climbers?

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Worksheet 3: Bottomless Problems

12. Julio (an 80 kg ice skating champion) and Grace are skating together on a rink at 3 m/s. Julio keeps asking Grace how much she weighs. Annoyed, Grace pushes away from Julio so that she speeds up to 4 m/s and he slows down to 2.25 m/s, in the same direction. The push lasts for 0.20 seconds. Friction, in the physics sense, is negligible in this drama.

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13. A 5000 kg truck rear-ends a 1200 kg car when the car was moving at 13 m/s. During the 0.15 second collision, the truck slows down from 14 m/s to 13.5 m/s. The road is dangerously slick, but not completely frictionless ( µ= 0.1 between the cars and the road).

Note: The sliding friction force between two surfaces can be approximated by using the coefficient of friction ( µ ) and the normal force between those same two surfaces (FN). The relationship is Ff = µFN.

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MTM Model Summary

New Concept Map

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