What is the overall efficiency of the compound machine which is used to raise heavy boxes consisting of ramps and pulley, over the pulley if the efficiency of the pulley is 90% ?

The correct answer to this question is B, 45%. This question would be asked on physics tests. The focus of this question is energy, work, and simple machines. In physics, energy is the capacity of doing work. There are various forms of energy including kinetic, thermal, and nuclear energy. Work is the action force completes and it moves energy.

Simple machines do work by using only one movement. Examples of simple machines include screws, wheels and axles, and wedges. These simple machines don't change the amount of work needed to do task, but they do change how work is done.