# A weston differential pulley block consists of a lower block and upper block. The upper block has two cogged grooves, one of which has a radius of 150 mm and the other a radius of 125 mm. If the efficiency of the machine is 50% calculate the effort required to raise a load of 1.5 kN.

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A weston differential pulley block consists of a lower block and upper block. The upper block has two cogged grooves, one of which has a radius of 150 mm and the other a radius of 125 mm. If the efficiency of the machine is 50% calculate the effort required to raise a load of 1.5 kN.

(a) 250 N

(b) 300 N

(c) 350 N

(d) 400 N

This question was posed to me in an internship interview.

Question is taken from Velocities in a Slider Crank Mechanism and Motion of a Link in portion Velocity in Mechanisms of Machine Kinematics

by (106k points)
The correct choice is (a) 250 N

Easiest explanation: We know that in case of a Weston differential pulley block,

V.R. = 2D/D – d = 2 x 300/300 -250 = 12

Using the relation, Efficiency = M.A./V.R. x 100

or, 50 = M.A./12 x 100

M.A. = 6

Again, M.A. = W/P

6 = 1.5 x 1000/ P

P = 250 N.

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