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Unformatted text preview: boland (kbb544) HW8 mackie (10611) 1 This printout should have 16 questions. Multiplechoice 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 3 s time interval. Its angular velocity at the end of this interval is 13 rad / s. What is the angular acceleration of the wheel? Note that the initial angular veloc ity is not zero. Correct answer: 19 . 2586 rad / s 2 . Explanation: Let : N = 20 , t = 3 s , and = 13 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 (13 rad / s) (3 s) 2 (20) (3 s) 2 = 19 . 2586 rad / s 2 . keywords: 002 10.0 points A copper block rests 21.0 cm from the center of a steel turntable. The coefficient of static friction between the block and the surface is 0.50. The turntable starts from rest and rotates with a constant angular acceleration of 0.60 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: 8 . 05487 s. Explanation: Let : r = 21 . 0 cm , s = 0 . 50 , = 0 . 60 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 . 5(9 . 81 m / s 2 ) (0 . 21 m) (0 . 6 rad / s 2 ) 2 = 8 . 05487 s . 003 10.0 points A rotating wheel requires 3 . 9 s to rotate through 43 . 1 rev. Its angular speed at the end of the 3 . 9 s interval is 108 . 8 rad / s. What is its constant angular acceleration? Assume the angular acceleration has the same sign as the angular velocity. boland (kbb544) HW8 mackie (10611) 2 Correct answer: 20 . 186 rad / s 2 . Explanation: Let : t = 3 . 9 s , = 43 . 1 rev , and f = 108 . 8 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 = (108 . 8 rad / s) (3 . 9 s) (43 . 1 rev) 2 1 rev = 153 . 515 rad , = 2 (153 . 515 rad) (3 . 9 s) 2 = 20 . 186 rad / s 2 ....
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 Spring '11
 MACKIE
 Physics, Acceleration

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