Question

A block and tackle of 6 pulley is used to raise a load of 30N steadily through a height of 3m. If the work done against friction is 100J and the total work done by the effort is 500J. Calculate:
a. The work done to raise the load
b. The efficiency of the system
c. The applied effort

Answer 1

work output is load weight * height raised = 30 N * 3 m = 90 Joules
work wasted in friction = 100 Joules
work input = 90 + 100 = 190 Joules
efficiency = 100 * work output / work input = 100 (90/190) = 47.4 %
If applied effort is the force in it is 1/6 * 190/3 = 10.6 Newtons