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Unformatted text preview: khounvivongsy (sk27799) – Homework 17 – Weathers – (17104) 1 This printout should have 10 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 10.0 points A woman with mass of 67 kg stands at the rim of a horizontal table having a moment of inertia of 620 kg m 2 and a radius of 2 . 8 m. The turntable is initially at rest and is free to rotate about a frictionless, vertical axis through its center. The woman then starts walking around the rim clockwise (as viewed from above the system) at a constant speed of 2 m / s relative to the Earth. With what angular speed does the turntable rotate? Correct answer: 0 . 605161 rad / s. Explanation: Basic Concepts: summationdisplay vector τ ext = d vector L d t The total momentum of a system is constant in our case, because there’s no external torque acting on the system. Therefore, the sum of the angular momenta of the woman and the turntable remains zero when the woman begins to walk. Hence L t = L w , and L t = m w v w r = (67 kg)(2 m / s)(2 . 8 m) = 375 . 2 kg m 2 / s where L t , L w are absolute values of the corre sponding vector quantities. Since L t = Iω t , we have ω t = L t I = (375 . 2 kg m 2 / s) (620 kg m 2 ) = 0 . 605161 rad / s 002 (part 2 of 2) 10.0 points How much work does the woman do ON THE TABLE to set it into motion? Correct answer: 113 . 528 J. Explanation: The work which the woman needs to perform to set the turntable into motion equals the change in kinetic energy of the turntable, i.e. W = I ω 2 t 2 = (620 kg m 2 ) (0 . 605161 rad / s) 2 2 = 113 . 528 J 003 (part 1 of 2) 10.0 points A small puck of mass 27 g and radius 14 cm slides along an air table with a speed of 1 . 4 m / s. It makes a glazing collision with a larger puck of radius 42 cm and mass 81 g (ini tially at rest) such that their rims just touch....
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This note was uploaded on 05/09/2010 for the course PHYS 1710 taught by Professor Weathers during the Spring '09 term at University of North Carolina Wilmington.
 Spring '09
 weathers
 mechanics, Mass, Work

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