posted by liz .
how much work is done by a crane that lowers 1000N of material 150m?
well the force is up but the motion is down so our answer will be negative.
- 150,000 Joules
That means that the weight does positive work on the crane. We could use that if we were smart to run a generator connected to the crane cable to charge the battery on the crane.
Regenerative braking systems on electric and hybrid vehicles work this way. Instead of forcing a plate agains the turning wheel to slow down, the axle turns a generator which chrges a battery. The torque to turn the generator slows the axle, and therefore the vehicle, down.