# Unit 4 Extra Credit

Either print this page and complete or (better yet) neatly show your answers on a separate page of paper. All answers must be expressed as complete sentences and/or all work shown to receive credit.

1. You are sitting at a baseball game when a foul ball comes in your direction. You prepare to catch it barehanded. In order to catch it safely, should you move your hands toward the ball, hold them still, or move them in the same direction as the moving ball? Why?

2. A 0.11g bullet leaves a pistol at 323 m/s, while a similar bullet leaves a rifle at 396 m/s. Explain the difference in exit speeds of the bullets.

3. During a "space walk", the tether connecting an astronaut to the space capsule breaks. Using a gas pistol, the astronaut manages to get back to the capsule. Explain.

4. Two trucks that look the same collide. One was originally at rest. The trucks stick together and move off at more than half the original speed of the moving truck. What can you say about the contents of the two trucks?

5. The velocity of a 600-kg auto is changed from +10.0 m/s to +44.0 m/s in 68.0 seconds by an applied, constant force.

a. What change in momentum does the force produce?

b. What is the magnitude of the force?

6. An animal-rescue plane flying due east at 36.0 m/s drops a bale of hay from an altitude of 60.0 m. If the bale of hay weighs 175 N, what is the momentum of the bale the moment it strikes the ground?

7. A 95 kg fullback, running at 8.2 m/s, collides in midair with a 128 - kg defensive tackle moving in the opposite direction. Both players end up with zero speed.

a. What was the fullback's momentum before the collision?

b. What was the change in the fullback's momentum?

c. What was the change in the tackle's momentum?

d. How fast was the tackle moving originally?

e. What was the tackle's original momentum?

8. A 50 kg women, riding on a 10 - kg cart, is moving east at 5.0 m/s. The women jumps off the cart and hits the ground at 7.0 m/s eastward, relative to the ground. Calculate the velocity of the cart after she jumps off.

Resources for physics students are available through links on the GBS Physics Home Page. Such resources include the Multimedia Physics Studios (a collection of animations and movies which illustrate key physics concepts) and The Physics Classroom (an online tutorial written in an easy-to-understand language).