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Classical Mechanics

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Work Done by Pulleys

CLMECH-FKX96B

A block and tackle is a system that uses pulleys to increase the force you can apply to lift heavy objects. It generally involves two pulleys around which you wrap a rope/cable/chain multiple times. Because tension is the same everywhere in the rope, each wrap multiplies your force.

M. Hawks. Created for Albert.io. Copyright 2016. All rights reserved.

If you have a block and tackle with three rope sections pulling up on the lower pulley as shown above, the force lifting the lower pulley is three times the tension you apply.

To lift the load $1\;m$ with this system, you need to pull the rope

and the work done on the load is

the work you do on the rope.