1. The problem statement, all variables and given/known data A simple pendulum is swinging. Its mass is m and its length is L. What is its gravitational potential energy if it is oriented at 30° with respect to the vertical? (Let gravitational potential energy be zero if it is in the vertical orientation). 2. Relevant equations U = mgh 3. The attempt at a solution Given mass = m and length = L, the only thing left is to solve for h. Since it is oriented 30° wrt vertical, then h = Lcos30°. So U = mgLcos30° But it's not the answer.