Unit 7, 8, 9 Physics Review

Transcription

1 Unit 7, 8, 9 Physics Review 1. A 2 kg mass is held 4 m above the ground. What is the approximate potential energy due to gravity of the mass with respect to the ground? a. 20 J. b. 40 J. c. 60 J. d. 80 J. e. none of these. 2. It takes 30 J to push a large box 4 m across a floor. Assuming that the push is in the same direction as the displacement, what is the size of the force on the box? a. 3 N. b. 7.5 N. c. 30 N. d. 120 N. e. none of these. 3. Which requires more energy: lifting a 50 kg sack vertically 2 meters or lifting a 25 kg sack vertically 4 meters? a. lifting the 50 kg sack. b. lifting the 25 kg sack. c. both require the same amount of work. 4. A car moving at 15 m/s skids to a stop in 20m. If the car travels at 30 m/s, how far will it skid, assuming the same constant braking force? a. 20 m. b. 40 m. c. 60 m. d. 80 m. e. 120 m. 5. Suppose W is the energy transferred stretching a spring from 0 to 0.10 m. The amount of work done stretching the same spring from 0.10 m to 0.20 m is: a. W b. 2W c. 3W d. 4W 6. A crate is dragged up a ramp at constant speed. The work done on the system can be accounted for by a. Eel b. Ek c. Eg d. Eint e. both c and d

2 For questions 12-14, consider the diagram representing a portion of an amusement park ride. A 100 kg car has 30,000 J of Potential Energy at point A. It moves down a frictionless track and comes to a stop as it compresses a huge spring at point D. 7. On the axes below, sketch the energy bar graphs when the car is at the indicated points. 8. How much kinetic energy does the car have at point C? Explain or calculate. 9. How fast is the car moving at point B? Show work. 10. Hulky and Bulky, two UPS workers, decide to race each other up a flight of stairs ( h = 4.0 m) at the warehouse. Hulky, whose mass is 120 kg, makes the climb in 3.0 s; while Bulky, 150 kg, took 4.0 s to make the climb. a. Who has more Eg at the top? b. Who exerted more power getting there?

3 In each of the pairs of diagrams below, a sphere attached to a string is swung in a flat circle (similar to the technique used in the lab). Examine each diagram carefully to note which variable has been changed. _ 11. How would the Fc of A compare to Fc of B? 12. How would the speed of A compare to that of B? *********************************************************** 13. How would the Fc of A compare to Fc of B? 14 How would the speed of A compare to that of B? *************************************************************** 15. How would the Fc of A compare to Fc of B? 16. How would the speed of A compare to that of B? c. A=B

4 17. A 400. kg roller coaster car is traveling at a constant speed of 12 m/s over a hill with a radius of curvature of 40. m. a. Draw a force diagram for the car on the diagram above. b. What is the normal force acting on the car at the top of the hill? Part II. For each of the situations outlined below in questions 1-4 compare (a>b, a<b, or a=b) the momentum of sphere A and sphere B. Then offer a brief explanation supporting your response.

5 6. Padded dashboards in cars are safer in an accident than non-padded ones because they a. increase the impact time. b. decrease the impulse on the occupant. c. decrease the change in momentum of the occupant. d. all of the above e. none of the above 7. A 1.0 kg chunk of putty moving at 1.0 m/s collides and sticks to a 5 kg bowling ball that is initially at rest. The magnitude of the momentum of the ball and putty after collision is a. more than 5.0 kgm/s. b. 5.0 kgm/s. c. 1.0 kgm/s. d. less than 1 kgm/s. e. 0.0 kgm/s. 8. A golf ball moving forward with a momentum of 1.0 kgm/s strikes and bounces backward off a heavy bowling ball that is initially at rest and free to move. The momentum of the bowling ball after collision is a. 1.0 kgm/s. b. more than 1.0 kgm/s. c. less than 1.0 kgm/s. d. not enough information provide e. none of the above 9. A bug collides with the windshield of a car traveling down the highway. Which experiences the greater change in momentum? a. it depends on the initial velocity of the bug b. the car c. the bug d. both experience the same change e. none of the above

6 10. A 150 g baseball is thrown toward home plate with a speed of 40. m/s. The batter hits the ball directly back at the pitcher with a speed of 50. m/s. a. Sketch a motion map to describe the motion of the baseball. b. What is the change in momentum of the ball? c. If the bat is in contact with the ball for 6.0 x 10-3 s, what is the average force exerted on the ball during the collision? d. How does the force exerted by the bat on the ball compare to the force exerted by the ball on the bat? Explain. 11. An 85.0 kg man, sitting in a 110 kg canoe, catches a 5.0 kg cooler, tossed at 5.0 m/s by a friend. a. Is the collision elastic or inelastic? Explain. b. What is the final velocity of the canoe?