1. The problem statement, all variables and given/known data A rotating objects motion can be described by its angle (θ). Given that an objects potential energy is U = 100(1-cosθ) and its kinetic energy is K = 10(dθ/dt)^2, form a second-order differential equation. Note that Total Energy = P + K, and that total energy does not change w.r.t. time. 2. Relevant equations E = U + K 3. The attempt at a solution E=U+K E= 100(1-cosθ) + 10(dθ/dt)^2 d(E)/dt = d/dt (100(1-cosθ)) + d/dt (10(dθ/dt)^2) 0 = 100sinθ + 20(dθ/dt)(d^2θ/dt^2) -100sinθ = 20(dθ/dt)(d^2θ/dt^2) -5sinθ =(dθ/dt)(d^2θ/dt^2) Hmm.. the answer should be -5sinθ = d^2θ/dt^2. What am I doing wrong? Any help would be appreciated.