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Unformatted text preview: Hood, Charles – Homework 8 – Due: Nov 2 2006, 11:00 pm – Inst: Jan Opyrchal 1 This printout should have 6 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points A penny of mass 3 . 1 g rests on a small 12 . 7 g block supported by a spinning disk. The disk has a radius of 12 cm. The coefficients of friction between block and disk are 0 . 801 (static) and 0 . 64 (kinetic) while those for the penny and block are 0 . 676 (static) and 0 . 45 (kinetic). The acceleration of gravity is 9 . 8 m / s 2 . Disk Penny Block r What is the maximum speed of the disk without the block and penny sliding? Correct answer: 70 . 9524 rpm. Explanation: The frictional force provides the centripetal force μmg = mv 2 r So the speed is v = √ μg r which is independent of mass. Since the static friction coefficient between the penny and block is smaller than that between the block and the disk, we use the coefficient of friction μ = 0 . 676....
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This note was uploaded on 03/22/2009 for the course PHYS 105 taught by Professor Ken during the Fall '08 term at NJIT.
 Fall '08
 KEN
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