Question

You want to prove the law of conservation of energy to a friend. For your demonstration you show that you can use a block and pulley machine to lift 100N with only 20N of Input Force. What would you say to your friend to explain how is this possible?

Answer 1

Pulleys help reduce the force needed by changing its direction; however, the direction of the movement is also changed. Therefore, the pulley's rope must be pulled further than the actual displacement of the block. Say if the block is raised by 1 meters, then the rope would have to be pulled 5 meters, thus conserving energy.