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Unformatted text preview: arellano (aa39398) Practice Homework Chapter 7 Solutions weathers (17101) 1 This printout should have 45 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points Two objects of same material are travelling near you. Object A is a 1 . 3 kg mass traveling 10 . 6 m / s; object B is a 2 kg mass traveling 5 m / s. Which object would make you feel worse if you are hit by it? 1. Unable to determine 2. A correct 3. the same 4. B Explanation: Let : m A = 1 . 3 kg , v A = 10 . 6 m / s , m V = 2 kg , and v B = 5 m / s . Compare their kinetic energies; the one with more energy will hurt you more severely. For object A, K A = 1 2 m A v 2 A = 1 2 (1 . 3 kg) (10 . 6 m / s) 2 = 73 . 034 J , and for object B, K B = 1 2 m B v 2 B = 1 2 (2 kg) (5 m / s) 2 = 25 J . K A > K B , so youll feel worse if you are hit by A. keywords: 002 (part 1 of 3) 10.0 points Two 4.2 g bullets are fired with speeds of 36.5 m/s and 82.1 m/s, respectively. a) What is the kinetic energy of the first bullet? Correct answer: 2 . 79772 J. Explanation: Basic Concept: K = 1 2 mv 2 Given: m 1 = 4 . 2 g v 1 = 36 . 5 m / s Solution: The kinetic energy of the first bullet is K 1 = 1 2 m 1 v 2 1 = 1 2 (4 . 2 g)(36 . 5 m / s) 2 1 kg 1000 g = 2 . 79772 J 003 (part 2 of 3) 10.0 points b) What is the kinetic energy of the second bullet? Correct answer: 14 . 1549 J. Explanation: Given: m 2 = 4 . 2 g v 2 = 82 . 1 m / s Solution: The kinetic energy of the sec ond bullet is K 2 = 1 2 m 2 v 2 2 = 1 2 (4 . 2 g)(82 . 1 m / s) 2 1 kg 1000 g = 14 . 1549 J arellano (aa39398) Practice Homework Chapter 7 Solutions weathers (17101) 2 004 (part 3 of 3) 10.0 points c) What is the ratio K 2 K 1 of their kinetic ener gies? Correct answer: 5 . 05942. Explanation: Solution: The ratio of the two kinetic energies is K 2 K 1 = 14 . 1549 J 2 . 79772 J = 5 . 05942 005 10.0 points An object is acted upon by a constant force which gives it a constant acceleration a . At a certain time t 1 , having started from rest at t = 0, it has kinetic energy K 1 . At what time t 2 has its kinetic energy dou bled? 1. t 2 = 5 t 1 2. t 2 = 1 . 5 t 1 3. t 2 = 16 t 1 4. None of the choices is correct. 5. t 2 = 2 t 1 correct 6. t 2 = 2 t 1 7. t 2 = 3 t 1 8. t 2 = 4 t 1 9. t 2 = 1 . 5 t 1 Explanation: v = a t , so K = 1 2 mv 2 = 1 2 ma 2 t 2 t 2 and K 2 K 1 = t 2 2 t 2 1 2 K 1 K 1 = t 2 2 t 2 1 t 2 t 1 = 2 . 006 10.0 points An outfielder throws a 1 . 32 kg baseball at a speed of 78 m / s and an initial angle of 11 . 8 . What is the kinetic energy of the ball at the highest point of its motion? Correct answer: 3847 . 52 J....
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