Practice Problem Set 3

1. Practice Problem Set 3 Momentum Impulse Energy

2. If both the mass and velocity of an object are doubled, its momentum • remains unchanged. • is doubled. • is quadrupled. • decreases.

3. Your friend says that impulse equals momentum. This statement isn’t correct, and the missing word is • work. • acceleration. • speed or velocity. • change.

4. A car and a large truck roll down a hill and reach the bottom at the same speed. Compared with the momentum of the car, the momentum of the truck is • less. • the same. • more. • none of the above.

5. A 10-kg dog chases a 0.5 kg squirrel at 10 m/s. Compared with the squirrel, the dog has • the same momentum. • 20 times as much momentum. • 10 times as much momentum. • 100 times as much momentum.

6. Zombies have invaded the campus, and you only have a baseball bat to defend yourself. You take a swing at an attacking zombie. When both the force and time of contact are doubled, the impulse on the zombie’s head will be: • unchanged. • doubled. • quadrupled. • decreased.

7. If the speed of a car doubles, what else doubles? • Its momentum. • Its kinetic energy. • Both of the above. • Neither of the above.

8. When you catch a fast-moving baseball with your bare hand, a good idea is to extend the amount of time it takes to bring the ball to rest. Why? • The impulse of the ball on your hand is reduced. • The force of the impact on your hand is reduced. • The change in momentum is reduced. • All of the above.

9. Whereas impulse involves force and time, work involves force and • energy. • acceleration. • distance. • power.

10. Yoda uses the Force to lift Luke Skywalker’s X-wing out of a swamp. He moves the X-wing 3 meters vertically with a force of 50,000 N. How much work did Yoda do on the X-wing? • 150,000 J • 150,000 N • 50,000 J • 50,000 N • 100,000 J • 100,000 N

11. How much potential energy was gained by the X-wing when it was lifted 3 meters? Assume that the mass of the X-wing is about 5,000 kg and that the gravity on Dagobah is the same as that on Earth. • 5,000 J • 100,000 J • 50,000 J • 15,000 J • 150,000 J

12. A 1-kg iron ball and a 10-kg iron ball are dropped from rest from the top of a building. Assume that air-resistance is negligible. Just before hitting the ground below, compared with the 1-kg ball, the 10-kg ball has • less momentum and KE. • the same momentum and KE. • 10 times as much momentum and 10 times as much KE. • 10 times as much momentum and 100 times as much KE.

13. When a car is braked to a stop, unless it is a hybrid, a majority of its kinetic energy is transformed into: • stopping energy. • potential energy. • mechanical energy. • heat.

14. A car increases its velocity from 50 km/h to 100 km/h. How much greater will its kinetic energy become? • Twice as much. • 4 times more. • It remains the same. • 50% more.

15. A car with a 70 kg test dummy inside is moving with a constant velocity of 20 m/s (~50 mph). The car experiences a head-on collision with a concrete wall and the test dummy inside is brought to rest in 0.5 seconds.

16. Calculate the initial momentum of the test dummy. Remember that the test dummy is moving at the same velocity as the car. • 70 kg·m/s • 20 kg·m/s • 1,400 kg·m/s • 0 kg·m/s • 700 kg·m/s

17. What is the change in momentum or impulse that is imparted on the test dummy when it is brought to rest in the collision? • 70 kg·m/s • 20 kg·m/s • 1,400 kg·m/s • 0 kg·m/s • 700 kg·m/s

18. Now that you know the change in momentum (impulse), calculate the average force that a seat belt would need to apply to the test dummy in order to bring it to rest in 0.5s • 2,800 N • 14,000 N • 700 N • 1,400 N • 70 N

19. If 1N is 0.225 lbs, then 2,800 N is 630 lbs being exerted on the dummy by the seat belt to bring it to rest in 0.5 s from 50 mph. • The duration or amount of time of impact must be greater in order to reduce the force of impact! • If time of impact was doubled (1 s), then how much would the force be?