A 56-kg housepainter stands on a 14-kg aluminum platform. The platform is attach

Question

A 56-kg housepainter stands on a 14-kg aluminum platform. The platform is attached to a rope that passes through an overhead pulley, which allows the painter to raise herself and the platform. (Ignore the mass of the pulley and any friction in the pulley.)

(a) With what force F must she pull down on the rope to accelerate herself and the platform upward at a rate of 0.79 m/s2?
__________ kN

(b) When her speed reaches 0.9 m/s, she pulls in such a way that she and the platform go up at a constant speed. What force is she exerting on the rope now? (Ignore the mass of the rope.)
__________ kN

Explanation / Answer

Given Data

Mass of the person = 56 kg

Mass of the platform = 14 kg

Solution

A)

Weight = mg = (56+14)*9.8 = 686

Force to act upward F‘ = ma = (56 + 14)*0.79 = 55.3 N

So total force required F = W + F’ = 686 + 55.3 = 741.3 N = 0.74 kN

B)

IF the lift moves at a constant speed then It means the applied force is equal to the weight

F’ = W = 686 N = 0.69 kN

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