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?

Question

jamesj · Answer

What must the set up of this pulley system be?  It must be that you have the rope looped around the pulley twice ... as in this ugly diagram |dw:1329861916667:dw|