A pulley system with 75% efficiency is set up to lift a 21kg bag of nails. The bag is lifted to a height of 2.3m by a person pulling on the rope with a force of 91.5N. What is the ideal mechanical advantage of this pulley system?
The mechanical advantage (MA) of a machine is a measure of how much the force is multiplied. It is the ratio of load/effort:
Because energy is conserved, this is done as a trade - off against the distance the effort moves compared with the load.
The ideal mechanical advantage (IMA) is the ratio of the distance moved by the effort/distance moved by the load.
If we divide MA by IMA we get:
In an ideal world this ratio would equal 1. However there are energy losses due to friction etc. We usually express this ratio in terms of efficiency
In this case: