Problem 1. We first consider a force applied perpendicular to a block of mass 5.

Question

Problem 1. We first consider a force applied perpendicular to a block of mass 5.00 kg placed against a frictionless wall. (a) Explain why the force cannot keep the block stationary, no matter how large F is. Now consider a force applied at an angle theta = 60.0 degree to the horizontal. The wall is still frictionless. (b) What is the magnitude F that will keep the block stationary? (Include a free-body diagram in your answer.) Now suppose the coefficient of static friction between the block and the wall is 0.300. The force is still applied as in part (b). (c) What are the minimum and maximum values of F that will keep the block stationary? (Include free-body diagrams for both cases.)

Explanation / Answer

F is balanced by normal force exerted by the wall on the block in opposote direction

but weight W is action in down ward direction

F net = W = mg = 5*9.8 = 49 Nin down

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Fsin60 = W

F = 49/sin60 = 56.58 N

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N = F*cos60

f = u*N = u* F*cos60

Fsin60 + f = W

Fsin60 + u*F*cos60 = W

F = W/(sin60 + ucos60) = 48.22 N.(min)

F = 58.56 (max)

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