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Unformatted text preview: markowitz (am45362) HW08 distler (56295) 1 This printout should have 21 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points A 6 m long, uniform ladder leans against a frictionless wall and makes an angle of 64 . 5 with the floor. The ladder has a mass 29 . 2 kg. A 75 . 92 kg man climbs 82% of the way to the top of the ladder when it slips and falls to the floor. What is the coefficient of static friction be tween the ladder and the floor? Correct answer: 0 . 348722. Explanation: Let : M = 29 . 2 kg , M m = 75 . 92 kg , R = 0 . 82 , and = 64 . 5 . summationdisplay F x = 0 requires the wall to exert a force equal in magnitude to the frictional force of ( M m + M ) g exerted by the floor. Applying torques on the ladder about the point where it touches the floor, ( M + M m ) g sin parenleftbigg M 2 + R M m parenrightbigg g cos = 0 2 ( M + M m ) sin = ( M 2 R M m ) cos = ( M 2 R M m ) cos 2 ( M + M m ) sin = [29 . 2 kg 2(0 . 82)(75 . 92 kg)] cos 64 . 5 2(29 . 2 kg + 75 . 92 kg) sin64 . 5 = . 348722 . 002 10.0 points Two masses of 25 kg and 16 kg are suspended by a pulley that has a radius of 14 cm and a mass of 8 kg. The cord has a negligible mass and causes the pulley to rotate without slipping. The pulley rotates without friction. The masses start from rest 1 . 3 m apart. 1 . 3 m 14 cm 8 kg 25 kg 16 kg Determine the speeds of the two masses as they pass each other. Treat the pulley as a uniform disk. The acceleration of gravity is 9 . 8 m / s 2 . Correct answer: 1 . 59625 m / s. Explanation: Let : M = 8 kg , R = 14 cm , m 1 = 25 kg , m 2 = 16 kg , and h = 1 . 3 m . From conservation of energy K 1 + K 2 + K disk = U m 1 v 2 2 + m 2 v 2 2 + M v 2 4 = ( m 1 m 2 ) g h 2 (2 m 1 + 2 m 2 + M ) v 2 = 2 ( m 1 m 2 ) g h, where h 2 is the height. Taking no slipping into account, v = radicalBigg 2 ( m 1 m 2 ) g h 2 ( m 1 + m 2 ) + M = radicalBigg 2 (25 kg 16 kg) (9 . 8 m / s 2 ) 2 (25 kg + 16 kg) + 8 kg 1 . 3 m = 1 . 59625 m / s . markowitz (am45362) HW08 distler (56295) 2 keywords: 003 10.0 points A rod of mass m and length L is hinged with a frictionless hinge at one end. The moment of inertia about the center of mass is 1 12 mL 2 . Attached to the end of the rod opposite to the hinge there is a mass of magnitude 2 m . The rod is released from rest in the horizontal position. L m 2 m What is the speed of the mass 2 m when the rod passes through the vertical position? Consider the mass at the end of the rod to be a point particle....
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This note was uploaded on 11/29/2011 for the course PHY 302K taught by Professor Kaplunovsky during the Spring '08 term at University of Texas at Austin.
 Spring '08
 Kaplunovsky
 Physics, Mass

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