Question

In a weston differential pulley block, the number of recesses in the smaller wheel is 9/10 of that of the larger wheel. If the efficiency of the machine is 50%, find the load lifted by an effort of 300N.

(a) 2000N

(b) 3000N

(c) 4000N

(d) none of the mentioned

I got this question during a job interview.

My doubt stems from Pulleys in portion Belt, Rope and Chain Drives of Machine Kinematics

Answer 1

Right option is (b) 3000N

For explanation: Let the recesses in the larger wheel, n1 = 10

Recesses in the smaller wheel, n2 = 9/10 x 10 = 9

V.R. = 2n1 /n1 – n2 = 2×10/10 – 9 = 20

and mechanical advantage M.A. = W/P

                              = W/300

efficiency = M.A./V.R.

  0.5 = W/300×20

W = 3000N.