problem11_94

University Physics with Modern Physics with Mastering Physics (11th Edition)

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11.94: a) Taking torques about the point where the rope is fastened to the ground, the lever arm of the applied force is 2 h and the lever arm of both the weight and the normal force is . tan ) ( so and , tan 2 θ h w n F h h - = Taking torques about the upper point (where the rope is attached to the post), . 2 h F h f = Using n f s μ and solving for F, , 400 36.9 tan 1 30 . 0 1 ) 400 ( 2 tan 1 1 2 1 1 s nN nN w F = ° - = - - - b) The above relations between become and , f n F , 5 2 , tan ) ( 5 3 F f h w n h F = - = and eliminating gives for solving and and F n f , tan 5 3 5 2 1 s - - w F and substitution of numerical values gives 750 N to two figures. c) If the force is
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Unformatted text preview: applied a distance y above the ground, the above relations become , ) ( , tan ) ( fh y h F h w n Fy =--= which become, on eliminating , and f n ( 29 ( 29 . tan 1 s --≥ h y h y F w As the term in square brackets approaches zero, the necessary force becomes unboundedly large. The limiting value of y is found by setting the term in square brackets equal to zero. Solving for y gives . 71 . 36.9 tan 30 . 9 . 36 tan tan tan = ° + ° = + = s h y...
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This document was uploaded on 02/05/2008.

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