Answer:
C. A pulley system is useful because it produces a large output force given a small input force.
Explanation:
When one or more moveable pulleys are used, the distance the rope travels is much greater than the height that the weight is lifted. In an efficient pulley system, the input work is nearly equal to the output work by conservation of energy. Therefore, if the input distance is larger than the output distance, the input force must be much less than the output force. This allows you to use a pulley to lift very heavy objects with relatively little force.
