hw8 - zhou (cz3574) HW8 mackie (10611) 1 This print-out...

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Unformatted text preview: zhou (cz3574) HW8 mackie (10611) 1 This print-out should have 16 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points A wheel rotating with a constant angular ac- celeration turns through 20 revolutions during a 4 s time interval. Its angular velocity at the end of this interval is 17 rad / s. What is the angular acceleration of the wheel? Note that the initial angular veloc- ity is not zero. Correct answer: 7 . 20796 rad / s 2 . Explanation: Let : N = 20 , t = 4 s , and = 17 rad / s . From kinematics t = f = f t and = N 2 ( ) , so = t + 1 2 t 2 2 N = ( f t ) t + 1 2 t 2 = f t 1 2 t 2 = 2 f t 2 N t 2 = 2 (17 rad / s) (4 s) 2 (20) (4 s) 2 = 7 . 20796 rad / s 2 . keywords: 002 10.0 points A copper block rests 44.9 cm from the center of a steel turntable. The coefficient of static friction between the block and the surface is 0.60. The turntable starts from rest and rotates with a constant angular acceleration of 0.40 rad/s 2 . After what time interval will the block start to slip on the turntable? The acceleration of gravity is 9 . 81 m / s 2 . Correct answer: 9 . 05163 s. Explanation: Let : r = 44 . 9 cm , s = 0 . 60 , = 0 . 40 rad / s 2 , and g = 9 . 81 m / s 2 . From kinematics f = i + t = t since i = 0 rad/s, F c = m a c = m ( r 2 f ) when the block starts to slip, and F s = s F n = s m g , so F c = F s m r 2 f = s m g r ( t ) 2 = s g t = radicalbigg s g r 2 = radicalBigg . 6(9 . 81 m / s 2 ) (0 . 449 m) (0 . 4 rad / s 2 ) 2 = 9 . 05163 s . 003 10.0 points A rotating wheel requires 2 . 86 s to rotate through 18 . 5 rev. Its angular speed at the end of the 2 . 86 s interval is 130 . 2 rad / s. What is its constant angular acceleration? Assume the angular acceleration has the same sign as the angular velocity. zhou (cz3574) HW8 mackie (10611) 2 Correct answer: 62 . 6273 rad / s 2 . Explanation: Let : t = 2 . 86 s , = 18 . 5 rev , and f = 130 . 2 rad / s . From kinematics f = + t = f t , so = t + 1 2 t 2 = ( f t ) t + 1 2 t 2 = t 1 2 t 2 = 2 ( t ) t 2 Since t = (130 . 2 rad / s) (2 . 86 s) (18 . 5 rev) 2 1 rev = 256 . 133 rad , = 2 (256 . 133 rad) (2 . 86 s) 2 = 62 . 6273 rad / s 2 ....
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This note was uploaded on 03/25/2011 for the course PHYS 122 taught by Professor Hiyishi during the Spring '10 term at Temple College.

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hw8 - zhou (cz3574) HW8 mackie (10611) 1 This print-out...

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