# ch6 - 31. (a) Free-body diagrams for the blocks A and C,...

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31 . (a) Free-body diagrams for the blocks A and C , considered as a single object, and for the block B are shown below. T is the magnitude of the tension force of the rope, F N is the magnitude of the normal force of the table on block A , f is the magnitude of the force of friction, W AC is the combined weight of blocks A and C (the magnitude of force & F gAC shown in the figure), and W B is the weight of block B (the magnitude of force & F gB shown). Assume the blocks are not moving. For the blocks on the table we take the x axis to be to the right and the y axis to be upward. From Newton’s second law, we have x component: T f = 0 y component: F N W AC = 0. For block B take the downward direction to be positive. Then Newton’s second law for that block is W B T = 0. The third equation gives T = W B and the first gives f = T = W B . The second equation gives F N = W AC . If sliding is not to occur, f must be less than µ s F N , or W B < s W AC . The smallest that W AC can be with the blocks still at rest is W AC = W B / s = (22 N)/(0.20) = 110 N.

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## This note was uploaded on 05/03/2010 for the course PHY PHY1003 taught by Professor Lee during the Spring '10 term at Yonsei University.

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ch6 - 31. (a) Free-body diagrams for the blocks A and C,...

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