Q: a man(40kg) walks up the stair of 3m high, how much work done by the man? wat i think is, the man experienced the gravitational pull, so the man should get a work done of mgh=40*9.81*3 J, is this correct? but the answer from the thermodynamic course tutorial Q is 0 J. why? 2nd Q: a man(40kg) walks up the stair of 3m high n walk down to floor again, how much work done by the man? for this Q, i will answer 0 J, because the displacement is 0m.