28 - hernandez (ejh742) oldhomework 28 Turner (58120) 1...

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Unformatted text preview: hernandez (ejh742) oldhomework 28 Turner (58120) 1 This print-out should have 11 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points The angle of the inclination is 38 . 5 , the outer part of the large pulley has a radius of 3 r and the inner part of the large pulley has a radius of r . 3 r r /2 r m T Find the mass m needed to balance the 1110 kg truck on the incline. The acceleration of gravity is 9 . 8 m / s 2 . Assume all pulleys are frictionless and massless and the cords are massless. Correct answer: 115 . 165 kg. Explanation: Let : = 38 . 5 , R = 3 r , and M = 1110 kg . Let T be the tension in the string around the inner part (radius = r ) of the pulley. Then from the force equilibrium for the small pulley at the truck 2 T- M g sin = 0 T = 1 2 M g sin = 1 2 (1110 kg) ( 9 . 8 m / s 2 ) sin 38 . 5 = 3385 . 86 N . From rotational equilibrium of the large pul- ley, summationdisplay = 0 mg (3 r )- T r = 0 m = T 3 g = 1 6 M sin = 1 6 (1110 kg) sin 38 . 5 = 115 . 165 kg . 002 10.0 points A massless beam supports two weights as shown. 680 N W L 4 L 4 L 2 L A B Find W such that the supporting force at A is zero. Correct answer: 340 N. Explanation: Let : W 1 = 680 N and F A = 0 . summationdisplay = 0, so for a fulcrum at B, W 1 L 4 = W L 2 W = 1 2 W 1 = 1 2 (680 N) = 340 N ....
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This note was uploaded on 06/14/2011 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas at Austin.

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28 - hernandez (ejh742) oldhomework 28 Turner (58120) 1...

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