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Unformatted text preview: Version PREVIEW OH10 Bradley (191) 1 This printout should have 17 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. This is Online Homework No. 10. It is due 06:00 AM Tuesday morning 4 November (Abu Dhabi Time), unless notified otherwise. Turntable Comes to a Stop 001 (part 1 of 2) 5.0 points The turntable of a record player rotates at a rate of 45 . 7 rev / min and takes 64 . 2 s to come to rest when switched off. Find the deceleration. Correct answer: 0 . 0745435 rad / s 2 . Explanation: Let : = 45 . 7 rev / min , t = 64 . 2 s , and f = 0 . The angular acceleration is = t = f t = t = 45 . 7 rev / min 64 . 2 s 2 1 rev 1 min 60 s = . 0745435 rad / s 2 , a deceleration of . 0745435 rad / s 2 . 002 (part 2 of 2) 5.0 points How many revolutions did it make before coming to rest? Correct answer: 24 . 4495 rev. Explanation: For a deceleration of , the angle is = t 1 2 t 2 = (45 . 7 rev / min)(64 . 2 s) 1 min 60 sec 1 2 (0 . 0745435 rad / s 2 ) (64 . 2 s) 2 1 rev 2 = 24 . 4495 rev . Rigid Rectangular System 02 003 (part 1 of 2) 5.0 points Four particles with masses 5 kg, 6 kg, 5 kg, and 2 kg are connected by rigid rods of neg ligible mass as shown. Aassume the system rotates in the xy plane about the z axis (ori gin, O ) with an angular speed of 4 rad / s. x y O 4 rad / s 9m 8 m 5 kg 6 kg 5 kg 2 kg Find the moment of inertia of the system about the z axis. Correct answer: 652 . 5 kg m 2 . Explanation: Let : m 1 = 5 kg , top left m 2 = 6 kg , bottom left m 3 = 5 kg , bottom right m 4 = 2 kg , top right w = 8 m , and h = 9 m . Each mass is a distance d = radicalBigg parenleftBig w 2 parenrightBig 2 + parenleftbigg h 2 parenrightbigg 2 = radicalbigg w 2 + h 2 4 from the axis of rotation, so I z = summationdisplay i m i r 2 i = d 2 summationdisplay i m i = w 2 + h 2 4 summationdisplay i m i Version PREVIEW OH10 Bradley (191) 2 = (8 m) 2 + (9 m) 2 4 (18 kg) = 652 . 5 kg m 2 . 004 (part 2 of 2) 5.0 points Find the rotational energy of the system about the z axis. Correct answer: 5220 J. Explanation: Let : = 4 rad / s . The rotational energy of the system is K = 1 2 I z 2 = 1 2 (652 . 5 kg m 2 ) (4 rad / s) 2 = 5220 J . Swinging Rod 02 005 10.0 points A massless rod of length L has a mass 2 m fastened at its center and another mass m fastened at one end. On the opposite end from the mass m , the rod is hinged with a frictionless hinge. The rod is released from rest from an initial horizontal position; then it swings down....
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This note was uploaded on 02/16/2009 for the course PYHS 191 taught by Professor Curtise during the Spring '08 term at Abilene Christian University.
 Spring '08
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