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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 you’ll 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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 Fall '10
 Weathers
 Force, Friction, Mass, Work, Arellano

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