A block is pressed against a vertical wall by a force F rightarrow, as the drawi

Question

A block is pressed against a vertical wall by a force F rightarrow, 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 theta is the same. Kinetic friction exists between the block and the wall, and the coefficient of kinetic friction is 0.260. The weight of the block is 43.0 N, and the directional angle for the force F rightarrow is theta = 36.0 degree. Determine the magnitude of F rightarrow when the block slides (a) up the wall and down the wall. P =

Explanation / Answer

when it moves up the wall :-

forces act down ward are

frictional force = P sin 36 andweight mg

forces act upward = P cos 36 and

it moves with constant velocity ,So, upward force =downward force

P cos 36 = mg + P sin 36

0.809 P = 43 N + 0.1528 P

P = 65.53 N

when it moves down ward :-

forces act up ward are

frictional force = P sin 37 and P cos 37

forces act downward = mg

it moves with constant velocity ,So, upward force =downward force

P cos 36 + P sin 36 = mg

0.809 P + 0.1528 P = 43 N

P = 44.71 N

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