1. The problem statement, all variables and given/known data A mass, m, is released from height, h, off a cliff. No air resistance. (a) How much Work is done on the mass by the gravitational force during the fall? (b) What is the change in PE of the mass-Earth system during the fall? (c) If that PE is taken to be zero at the ground, what is its value when the mass is released? (d) If, instead, the PE is taken to be zero at the release point, then what is its value when the mass reaches the ground? 2. Relevant equations W= F*d PE = m*g*y 3. The attempt at a solution (a) W= 9.8*m*h, understand that one. (b) Change in PE is PEfinal-PEinitial, which is 0 - 9.8*m*h. (c) This is where I get a bit lost.. I would think its the same answer as (b) because I was already assuming that the PEfinal is going to be zero when on the ground anyway. I peeked at the answers and this one = 9.8*m*h Positive... (d) Same problem here.. I'm thinking that PEfinal-PEinitial would be 9.8*m*h - 0. But again it's reversed than how I'm getting it. This answer is -9.8*m*h Any help is appreciated, thanks.