Question

A person is able to pull a rope with a force of 700 N. What is the minimum number of fixed and moveable pulleys that the person will require to lift up a 27,800 N elephant? Assume the pulleys themselves are weightless and the system has 100% efficiency.

Answer 1

Each pulley reduces the extra effort compulsory to lift the elephant (light and 100% efficiency). If the elephant "weighs" 27,800 N and the person can apply 700 N,
27,800 / 700 = 39.7 which is about 40 N.
The answer that offers a combined # of 40 pulleys is computed by:
40 / 2 = 20

Therefore the answer is 20 fixed and 20 moveable.