A block is pressed against a vertical wall by a force P, as the drawing shows Th

Question

A block is pressed against a vertical wall by a force P, as the drawing shows This force can either push the block upward at a constant velocity or allow it to slide downward at a constant velocity. The magnitude of the force is different in the two cases, while the directional angle is the same. Kinetic friction exists between the block and the wall, and the coefficient of kinetic n is 280 The eight of the blockis 53 N and the directional angle for the e 47°, Determine the magnitude of P when the block slides the following ways (a) up the wall (b) down the wall

Explanation / Answer

Solution,

A)

when it moves up the wall,

frictional force = u x P sin 47 and weight mg

forces act upward = P cos 47 and it moves with constant velocity. So, upward force = downward force

P cos 47 = mg + uP sin 47

0.682 P = 53 + 0.205 P

P = 111.06 N

B)

when it moves down ward,

frictional force = u P sin 47 and P cos 47

forces act downward = mg

P cos 47+ P sin 47 = mg

0.682 P + 0.205 P = 53 N

P = 59.77 N

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