A block and tackle system of pulleys consisting of 4 pulleys is used to raise a load of 500N through a height of 20m. If the total work done against friction is 800j. Determine the efficiency of the machine
work done on load ... 500N * 20m = 10 kJ
efficiency = (work on load) / [(work on load) + (work against friction)]
... 10 kJ / (10 kJ + .8 kJ) = ? %