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Unformatted text preview: pasha (sep635) HW 10-1 Antoniewicz (56445) 1 This print-out should have 18 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 2) 10.0 points A ball whose mass is 0 . 7 kg hits the floor with a speed of 9 m / s and rebounds upward with a speed of 6 m / s. The ball was in contact with the floor for 0 . 8 ms. Use g = 9 . 8 m / s 2 . Calculate the magnitude of the gravita- tional force that the Earth exerts on the ball. Correct answer: 6 . 86 N. Explanation: The magnitude of the gravitational force on the ball is given by F grav = mg = (0 . 7 kg)(9 . 8 m / s 2 ) = 6 . 86 N . 002 (part 2 of 2) 10.0 points What was the average magnitude of the force exerted on the ball by the floor? Correct answer: 13131 . 9 N. Explanation: We can write ~ F net = ~ p t F net ,y = m ( v f,y- v i,y ) t = (0 . 7 kg)(6 m / s- (- 9 m / s)) . 8 ms = 13125 N . Then F net ,y = F floor ,y- mg F floor ,y = F net ,y + mg = 13125 N + 6 . 86 N = 13131 . 9 N . 003 10.0 points Two asteroids in outer space collide and stick together. The mass of each asteroid, and the velocity of each asteroid before the im- pact, are known. To find the momentum of the stuck-together asteroids after the impact, what approach would be useful? 1. It depends on whether or not the speed of the asteroids was near the speed of light. 2. Use the relationship among velocity, dis- placement, and time. 3. Use the Momentum Principle. correct 4. It depends on whether the collision was elastic or inelastic. 5. Use the Energy Principle. Explanation: We should use the Momentum Principle. During the time interval of the collision, ~ F and the momentum of the system of two as- teroids is conserved. 004 (part 1 of 9) 3.0 points Object A has mass m A = 8 . 5 kg and initial momentum ~ p A,i = h 18 ,- 9 , i kg m / s , just before it strikes object B , which has mass m B = 15 kg. Just before the collisions, object B has initial momentum ~ p B,i = h 11 , 15 , i kg m / s ....
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This note was uploaded on 11/17/2011 for the course PHY 303K taught by Professor Turner during the Fall '08 term at University of Texas at Austin.
- Fall '08