Question

A person weighing 600 N platform attached to the lower block of a system of 5 pulleys arranged in the second system. The platform and the lower block weigh 100N. The man himself supports by exerting a downward pull at the free end of the rope. Neglecting friction, the minimum pull of the man will be

(a) 1000 N

(b) 200 N

(c) 116.7 N

(d) none of the mentioned

I had been asked this question in an international level competition.

I need to ask this question from Pulleys in portion Belt, Rope and Chain Drives of Machine Kinematics

Answer 1

Correct option is (c) 116.7 N

The explanation is: n = total number of pulleys in the system = 5

             W = 600 N

Weight of the lower block and platform = 100 N

Total weight = 600 + 100 = 700 N

Let the pull exerted by the man be P newton.

Due to this pull the effective load on the lower platform will reduce to (700 – P)

nP = effective load = 700 – P

therefore, 5P = 700 -P

           5P = 700

           P  = 116.7 N.