1. The problem statement, all variables and given/known data A particle moving along the x-axis is subject to a conservative force such that the potential energy of the particle is given by U(x,y)=2x + x^3 where x and y are in meters, U is in joules. When the particle moves from (2,0) to the origin, the work done by the conservatice force is: A) b) c) d) (the choices don't matter... I have the right value, wrong sign) 2. Relevant equations delta(U) = change in potential energy. 3. The attempt at a solution Okay, my real question here is: What does this notation U(x,y) really mean? And I checked the solution for this problem, and it says U(initial) - U(final)...... Why is this? Since when is the change in a value equal to initial - final ?