1. The problem statement, all variables and given/known data A thin rod, of length L = 2.00 m and negligible mass, that can pivot about one end to rotate in a vertical circle. A ball of mass m = 5.00 kg is attached to the other end. The rod is pulled aside to angle theta = 30 and released with initial velocity v= 0. As the ball descends to its lowest point, (a) how much work does the gravitational force do on it and b) what is the change in the gravitational potental energy of the ball - Earth system?.. etc. 2. Relevant equations 3. The attempt at a solution In the solution, they show W = 5 x 9.8 x 2(1- cos30) where do they get the 1-cos30??