1. The problem statement, all variables and given/known data A cylinder with mass M and radius R and moment of inertia I is standing on a rough surface (the left part of the triangle). A box with mass m is standing on a smooth surface (right part of the triangle). The cylinger and box is connected by a massless rope over a massless pulley. The cylinder starts from rest and then rolls. Find the velocity of the box at the top of the triangle. 2. Relevant equations Kinetic rotational and translational energy Potential energy 3. The attempt at a solution I tried to solve this and then I looked at my facits but there was one thing I did not take account for in my energy equation. This is my facit (point of reference for potential energy is at their start position): Where "1" is their start positions and "2" is when the box reaches the top of the triangle. The thing that I have problem figuring out is this part: I know it's supposed to be the potential energy of the cylinder when the box reaches the top, but I have no idea how they reached that. I've been looking at the drawing for an hour and can't figure it out.