# Unit 5 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. Why does an automobile moving at constant velocity have to keep burning fuel to maintain motion?

2. The potential energy acquired in driving to the top of a mountain is the same whether the road goes straight up or zigzags in gradual slopes. Why then do most mountain roads wind up gradually rather than rising straight up with a steep slope?

3. A light truck and a heavy truck are traveling the same speed. It is easier for the light truck to stop. Explain why.

4. A light truck and a heavy truck are moving with the same momentum. Which requires the most work to stop? Explain.

5. When a rifle with a long barrel is fired, the force of expanding gases acts on the bullet for a longer distance. What effect does this have on the velocity of the emerging bullet?

6. Explain why long range cannons have long barrels.

7. A flight attendant and a passenger toss a ball back and forth in a moving airplane. Does the kinetic 9. At what point in its motion is the kinetic energy of a pendulum bob at a maximum? ______ At what point is its potential energy at a maximum? ________ When its kinetic energy is half its maximum value, how much potential energy does it have?

8. A physics instructor demonstrates energy conservation by releasing a heavy pendulum bob and allowing it to swing to and fro. What would happen if in her exuberance, she gave the bob a slight shove as it left her nose? Explain.

9. In the absence of air resistance, a ball thrown vertically upward with a certain initial kinetic energy will return to its original level with the same kinetic energy. When air resistance is a factor affecting the ball, will it return to its original height with the same, less, or more kinetic energy? Does this answer contradict the conservation of energy principle? Explain.

10. A child on a rooftop throws two identical balls with the same initial speed in opposite directions - up and down. When the two balls strike the ground, which ball is traveling with the greater speed? Explain. (Be careful.)

11. Discuss the design of a roller coaster in terms of conservation of energy.

12. Two classmates are discussing the design of a roller coaster. One classmate says that each summit must be lower than the previous one. The other classmate says that this is nonsense, for as long as the first one is the highest it doesn't matter what height of the others are. What would you say?

13. You tell your friend that no machine can possibly put out more energy than is put into it. Your friend states that a nuclear reactor puts out more energy than is put into it. What do you say?

14. A ball dropped into a steel plate loses 10 percent of its kinetic energy with each bounce. Estimate the number of bounces the ball will make before it fails to rise to half its initial height.

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).