A 10-ft beam, weighing 1280 lb. is to be moved to the left onto the platform as

Question

A 10-ft beam, weighing 1280 lb. is to be moved to the left onto the platform as shown. A horizontal force P is applied to the dolly, which is mounted on frictionless wheels. The coefficients of friction between all surfaces are mu_s = 0.30 and mu_k = 0.25. and initially, x = 2 ft. The top surface of the dolly is slightly higher than the platform. If two 175-lb workers stand on the beam at B, determine how far the beam can be moved to the left. (Round the final answer to two decimal places.) The beam moves ft to the left. A flat belt is used to transmit a couple from drum R to drum A. Knowing that the coefficient of static friction is 0.40 and that the allowable belt tension is 480 N, determine the largest couple that can be exerted on drum A. (Round the final answer to one decimal place.). The largest couple that can be exerted on drum A is__________N . m.

Explanation / Answer

for second question

here

theta A = 180deg + 30deg = pie + pie / 6 = 7pie / 6

theta B = 180deg - 30deg = pie - pie/6 = 5pie / 6

since (theta B) < (theta A) slipping will impend first on B(friction cofficients being equal )

T2 = Tmax = T1 * e^(u * theta B)

480 = T1 * e^(0.4 * 5pie/6)

T1 = 168.53 N

then

sum of Ma = 0 ;

Ma + 0.12 * (T1 - T2) = 0

Ma = 0.12 * (480 - 168.53) = 37.37 Nm

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