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Unformatted text preview: lai (yl8859) HW15 Ross (15200) 1 This printout should have 11 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 3) 10.0 points As a result of friction, the angular speed of a wheel c hanges with time according to d d t = e t , where and are constants. The angular speed changes from an initial angular speed of 5 . 53 rad / s to 4 . 73 rad / s in 3 . 92 s . Determine the magnitude of the angular acceleration after 1 . 88 s. Correct answer: 0 . 204525 rad / s 2 . Explanation: Let : = 5 . 53 rad / s , t = 0 , 2 = 4 . 73 rad / s , t 2 = 3 . 92 s , and t 3 = 1 . 88 s . The equation of motion is = e t , so 2 = e t 2 ln parenleftbigg 2 parenrightbigg = t 2 = ln parenleftbigg 2 parenrightbigg t 2 = ln parenleftbigg 4 . 73 rad / s 5 . 53 rad / s parenrightbigg 3 . 92 s = 0 . 0398629 s 1 . Thus the angular acceleration at t 3 is ( t 3 ) = d dt = ( ) e t 3 = (5 . 53 rad / s) (0 . 0398629 s 1 ) e (0 . 0398629 s 1 ) (1 . 88 s) = . 204525 rad / s 2 bardbl vector ( t 3 ) bardbl = . 204525 rad / s 2 . 002 (part 2 of 3) 10.0 points How many revolutions does the wheel make after 1 . 15 s ? Correct answer: 0 . 989296 rev. Explanation: Let : t f = 1 . 15 s . = integraldisplay t f e t dt = integraldisplay t f e t ( dt ) = e t vextendsingle vextendsingle vextendsingle...
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This note was uploaded on 02/24/2011 for the course PHYS 152 taught by Professor Button during the Winter '08 term at IUPUI.
 Winter '08
 BUTTON
 mechanics, Friction

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