An 8 ft long ladder has seven rungs. The rungs are spaced 1 ft apart, and the to
ID: 1852005 • Letter: A
Question
An 8 ft long ladder has seven rungs. The rungs are spaced 1 ft apart, and the top and bottom rungs are 1 ft from their respective ends of the ladder. The top of the ladder has a roller. Neglect the weight of the ladder and assume the worker?s hand applies no force to the ladder. If the worker weighs 140 lb and stands on the middle rung, determine the minimum value of the coefficient of friction so that the ladder does not slide.
An 8 ft long ladder has seven rungs. The rungs are spaced 1 ft apart, and the top and bottom rungs are 1 ft from their respective ends of the ladder. The top of the ladder has a roller. Neglect the weight of the ladder and assume the worker?s hand applies no force to the ladder. If the worker weighs 140 lb and stands on the middle rung, determine the minimum value of the coefficient of friction so that the ladder does not slide.Explanation / Answer
Assume there is no friction at the roller.
Fy =0: W - Ay =0 => Ay = 140 lb
MB =0: Ax(8 sin60) - Ay(8 cos 60) +W (4 cos60) =0
Ax = 40.4145 lb
s = Ax/Ay = 0.2887
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