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Name: ________________________ Class: ___________________ Date: __________ Exam 3--PHYS 101--F14--Chapters 5 & 6 Multiple Choice Identify the choice that best completes the statement or answers the question. 5. A weight lifter lifts a 275 kg barbell from the ground to a height of 2.4 m. How much work has he done in lifting the barbell, and how much work is required to hold the barbell at that height? 1. Which of these following is a conservative force? a. Air resistance b. Convection c. Gravity d. Friction 2. A massless spring initially compressed by a displacement of 2 centimeters is now compressed by 4 centimeters. How has the potential energy of this system changed? a. The potential energy has not changed. b. The potential energy has increased by 2 joules. c. The potential energy has quadrupled. d. The potential energy has doubled. a. b. c. d. 3. A 2000 kg experimental car can accelerate from 0 to 30 m/s in 6 s. What is the average power of the engine needed to achieve this acceleration? a. b. c. d. 1145 J and 0 J, respectively 6600 J and 0 J, respectively 1146 J and 3234 J, respectively 6600 J and 6600 J, respectively 6. A 40 kg block is resting at a height of 5 m off the ground. If the block is released and falls to the ground, which of the following is closest to its total mechanical energy (including potential and kinetic energies) at a height of 2m, assuming air resistance is negligible. 150 W 150,000 W 900 W 900,000 W a. b. c. d. 4. A tractor pulls a log with a mass of 500 kg along the ground for 100 m. The rope (between the tractor and the log) makes an angle of 30 degrees with the ground and is acted on by a tensile force of 5000 N. How much work does the tractor perform in this scenario? a. 433 kJ b. 250 kJ c. 500 kJ d. 289 kJ 800 J 400 J 2000 J 0J 7. When an increase in speed doubles the kinetic energy of a moving body, its momentum a. increases, but less than doubles. b. doubles. c. more than doubles. d. depends on factors not stated. 1 11. For the previous problem, what is the speed of the particle at point C, where the height is 0m? 8. When an increase in speed doubles the momentum of a moving body, its kinetic energy a. increases, but less than doubles. b. doubles. c. more than doubles. d. depends on factors not stated. 9. A 800 kg car is traveling at 12 m/s along a horizontal road when the brakes are applied.The car skids to a stop in 4.0 s.How much kinetic energy does the car lose in this time? a. b. c. d. 12 m/s 7.1 m/s 6.4 m/s 14 m/s 12. These four blocks are all moving to the right. Which of the forces is doing zero work on the block? a. b. c. d. e. 4.8x106 J 3.8x104 J 1.4x104 J 5.8x104 J 9.6x103 J a. b. c. d. e. 10. A particle is on a frictionless track as shown here. The particle is initially at a height of 10 m and is not moving. The particle is released. What is the speed of the particle at point (b), which is 2 m high? a. b. c. d. a b c d more than one is doing zero work 13. A spring has a spring constant of 100 N/m; the mass of the block is 2 kg. You compress the spring by 10 cm as in this figure. The spring causes the block to move to the right; then the block leaves the spring and continues along on a frictionless surface. What is the velocity of the block after it leaves the spring? a. b. c. d. 13 m/s 8.9 m/s 10. m/s 2.0 m/s 2 0.1 m/s 0.3 m/s 0.5 m/s 0.7 m/s 17. Alex throws a 0.15-kg rubber ball down onto the floor. The ball's speed just before impact is 6.5 m/s, and just after is 3.5 m/s. The impact lasts for 0.1 s. What is the magnitude of the force acting on the ball? 14. Two trailers, X with mass 500 kg and Y with mass 2000 kg, are being pulled at the same speed. The ratio of the kinetic energy of Y to that of X is (ie. KEY:KEX): a. b. c. d. e. 1:1 2:1 4:1 9:1 16:1 15. A 1.0 kg block is travelling to the right at 3.0 m/s. It collides with a stationary 2.0 kg block. The 2.0 kg block now has a speed of 1.0 m/s to the right. What is the final velocity of the 1.0 kg block? a. b. c. d. a. b. c. d. 18. Which of these statements is true? a. energy is a vector; momentum is scalar b. energy is a scalar quantity; momentum is a vector c. both energy and momentum are vector quantities d. both energy and momentum are scalar quantities 1.0 m/s 0.5 m/s 2.0 m/s 3.0 m/s 19. A raft with mass of 100 kg is drifting at 4 m/s. A person drops on to the raft from a tree branch over the river; the person has a mass of 100 kg. What is the speed of the raft after the person jumps on? 16. A force of 100 N acts on a 100 kg boulder for 2 seconds; the same force acts on a 1 kg stone for 2 seconds. Which experiences the larger change in momentum? a. b. c. 15 N 100 N 35 N 20 N the boulder the stone both the same a. b. c. d. 4 m/s 2 m/s 10 m/s 8 m/s 20. In which of these collisions is a. cars colliding b. people colliding c. gas particles colliding d. all of these 3 energy conserved? 25. Which of these bodies has the largest energy? I. Mass 3M and speed V II. Mass M and speed 4V III. Mass 3M and speed 2V IV. Mass 2M and speed 3V a. II & III b. III & IV c. IV alone d. I and II e. III alone 21. An inelastic collision is one in which a. only momentum is conserved b. only energy is conserved c. both energy and momentum are conserved d. neither energy or momentum are conserved 22. A 0.12-kg ball is moving at 6 m/s when it is hit by a bat, causing it to reverse direction and have a speed of 14 m/s. What is the magnitude of the change in the momentum of the ball? 26. Gwen weighs 150 pounds. Amy weighs 50 pounds. They are standing still on ice and push off from one another. Amy goes away at 10 m/s. What is Gwen’s speed? a. 3 m/s b. 30 m/s c. 7 m/s d. 9 m/s a. b. c. d. 2.4 kg⋅m/s 1.3 kg⋅m/s 0.42 kg⋅m/s 0.39 kg⋅m/s 23. A system of particles has an energy of zero. Which of these statements is true about the momentum of the system? a. b. c. d. the momentum is zero the momentum is negative the momentum is positive not enough information 24. Which of these bodies has the largest momentum? I. Mass 3M and speed V II. Mass M and speed 4V III. Mass 3M and speed 2V IV. Mass 2M and speed 3V a. II & III b. III & IV c. IV alone d. I and II e. III alone 4 ID: A Exam 3--PHYS 101--F14--Chapters 5 & 6 Answer Section MULTIPLE CHOICE 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: C C B A B C A C D A D A D C A C A B B C A A A B C A PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 DIF: 2 TOP: 6.1 Momentum and Impulse 1