Name: Physics 644 Date: / / Review: Work, Energy, Power Work. 1. What are the two important variables for work? (hint: look at the equation!

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1 Name: Physics 644 Date: / / Review: Work, Energy, Power Work 1. What are the two important variables for work? (hint: look at the equation!) 2. Is work done in the following situations? A. Is work done if you lift a 2 N book straight up 2 meters at a constant speed? B. Is work done if you pull a wagon 20 meters with a force of 10 N? C. Is work done if you spend 5 hours studying for a quiz? D. Is work done if you carry a 5 N tray a horizontal distance of 10 meters at a constant speed? E. Is work done if you push as hard as you can against a cement wall for two minutes but it doesn t move? 3. How much work is done if you push a crate with a constant force of 20 N for 10 meters? Page 1 of 8

2 4. How much work is done if you carry a 10 N box a horizontal distance of 25 meters? Power 5. Who is more powerful: someone who can do 100 J of work in 5 seconds or someone who can do 100 J of work in 50 seconds? Explain. 6. Who is more powerful: someone who can do 10 J of work in 10 seconds or someone who can do 100 J of work in 10 seconds? 7. What is your power output if you can do 600 J of work in 15 seconds? Page 2 of 8

3 Energy 8. What does kinetic energy depend upon? (choose between: speed or height) 9. What does potential energy depend upon? (choose between: speed or height) 10. Can an object that is at rest have energy? Give an example to support your answer. 11. What kind of energy does an apple that is hanging (at rest) in a tree have? 12. What kind of energy does an apple that has fallen out of a tree have just before it hits the ground? 13. Which has more potential energy: a 25 N kitten that is sitting on the counter 1 m above the ground or a 50 N cat who is also 1 m above the ground? 14. Which has more potential energy: a 50 N cat that is 1 m above the ground or a 50 N cat who has climbed a tree and is 10 m above the ground? Page 3 of 8

4 15. Find the equation for kinetic energy on your MCAS formula sheet and copy it into the space below: KE = 1 2 mv2 16. Which has more kinetic energy: a mouse who is running at 2 m/s or a cat who is running at 2 m/s? 17. Which has more kinetic energy: a 5 kg cat who is walking at 1 m/s or a 5 kg cat who is running at 3 m/s? Page 4 of 8

5 MCAS Questions: The following questions are taken from past MCAS exams. Please circle the correct answer for multiple choice questions. 18. (2004, grade 9, #17) A skateboarder travels from location 1 to location 4 as shown below At which location does the skateboarder have the most kinetic energy and the least potential energy? A. 1 B. 2 C. 3 D (2005, grade 8, #9) The diagram below represents a diver s motion from the top of a high diving board into a pool of water. At which labeled point does the diver have the least potential energy? A. 1 B. 2 C. 3 D. 4 Page 5 of 8

6 20. (2004, grade 9, #12) At a weightlifting competition, two competitors lifted the same weight to the same height. The second competitor accomplished the lift in 2 seconds faster than the first competitor. This demonstrated that the second competitor had more A. energy than the first. B. inertia than the first. C. power than the first. D. work than the first. 21. (2004, grade 9, #2) An archer pulls back the bowstring to prepare to shoot an arrow as shown below. She uses an average force of 40 N, moving the bowstring 0.2 m. How much energy is stored in the bow? A. 8 J B. 16 J C. 24 J D. 36 J 22. (2005, grade 9, #19) A man ran on a treadmill for 1,800 seconds. At the end of his run, the treadmill indicated his energy output as 240,000 J. What average power did he generate? A. 666 W B. 133 W C. 66 W D. 7 W Page 6 of 8

7 23. (2006, grade 9, #44) An astronaut drops a 1.0 kg object and a 5.0 kg object on the Moon. Both objects fall a total distance of 2.0 m vertically. Which of the following best describes the objects after they have fallen a distance of 1.0 m? A. They have each lost kinetic energy. B. They have each gained the same amount of potential energy. C. They have each lost the same amount of potential energy. D. They have each gained one-half of the maximum kinetic energy. 24. (2006, grade 9, #24) The figure below shows a wagon that moves from point X to point Y. Which of the following best describes the wagon s change in energy as it coasts from point X to point Y? A. The wagon has the same kinetic energy at point Y and a point X. B. The wagon has more kinetic energy at point Y than at point X. C. The wagon has the same gravitational potential energy at point Y and at point X. D. The wagon has more gravitational potential energy at point Y than at point X. 25. (2006, grade 9, #31) Which of the following describes the mechanical energy of a cart at rest at the top of a steep hill? A. The cart has no mechanical energy. B. The cart s mechanical energy is all kinetic. C. The cart s mechanical energy is all potential. D. The cart s mechanical energy is half potential and half kinetic. Page 7 of 8

8 The next item is an OPEN RESPONSE QUESTION. BE SURE TO ANSWER AND LABEL ALL PARTS OF THE QUESTION. Show all your work (diagrams, tables, or computations) in the space provided. If you do the work in your head, explain in writing how you did the work. 26. (2005, grade 9, #8) The figure below shows a tennis ball bouncing from point 1 to point 5. The tennis ball bounces up from point 1 as shown in the figure to a maximum height labeled as point 2. The ball then bounces a few times. Neglect any horizontal motion. A. Describe the kinetic and gravitational potential energy changes of the ball that occur between points 1 and 2. B. Describe the kinetic and gravitational potential energy changes of the ball that occur between points 2 and 3. C. Compare the kinetic energy of the ball at points 3 and 4. D. The tennis ball has less energy at point 5 than it had at point 3. Explain what happened to the energy the ball had at point 3. Page 8 of 8