quick question

[ShakeWell]

ok, tell me if i'm wrong:

the questions asks:
How much total mechanical work does a eight lifter do in 10 repetitions of lifting (and lowering) 200 kg to a height of 1.0m?

I'm thinking, since the final total displacement is zero, the answer is 0 right?

[HallsofIvy]

The "total mechanical work" is the change in potential energy (and here, since the weight is returned to its initial position that is 0) only for a "conservative" force (i.e. no friction). Of course, gravity is conservative but, in general, the force supplied by muscles is not. I don't think it is possible to give a definite answer without knowing precisely what assumptions are made. Exactly what the total mechanical work is depends a lot on how it is moved. Many texts would not call the work the muscles have to do "mechanical" work. While I think there is a very good argument for "0 work", I recommend you discuss this with your teacher!