1. The problem statement, all variables and given/known data I got into a disagreement with a fellow student today. He insisted that it's possible to simplify the system on the right as the system on the left. I agree with him that the difference in potential energy (and, therefore, the kinetic energy) is the same but I insist that the final velocities of the two systems will differ. We ended up surveying 6 different physics / engineering students and all agreed with him at a glance. One did text me tonight that he's on my side after having done the problem on paper. All of the engineering and physics profs were at lunch and couldn't be reached. I intend to ask at least one of them in Physics 2 in the morning. Given: Release both systems from rest (initial velocity = 0). Assume no moment of inertia for pulleys, massless, non-stretchy cable. You can simplify the box with mass=0 as an empty rope end if you wish. 2. Relevant equations I am basing my predicted results on energy theory, since there are no outside forces acting on the system, Ei = Ef. 3. The attempt at a solution I worked this out on paper and believe it confirms my intuition that you cannot equate the two systems to simplify a problem. Thanks for your input!