The problem statement, all variables and given/known data A rigid, massless rod has three particles with equal masses attached to it as shown in Figure P11.45. The rod is free to rotate in a vertical plane about a frictionless axle perpendicular to the rod through the point P, and is released from rest in the horizontal position at t = 0. Assuming m and d are known, find (a) the moment of inertia of the system (rod plus particles) about the pivot, (b) the torque acting on the system at t = 0, (c) the angular acceleration of the system at t = 0, (d) the linear acceleration of the particle labeled 3 at t = 0, (e) the maximum kinetic energy of the system, (f) the maximum angular speed reached by the rod, (g) the maximum angular momentum of the system, and (h) the maximum speed reached by the particle labeled 2. The attempt at a solution I have found moment of inertia, I = 7md^2/3 torque = mgd k, where k is unit vector angular accel = 3g/7d accel = 2g/7 but i dont know how to solve for maximum kinetic energy. Thinking of consv of energy, and from the COE eqn, there seems to be potential energy. But i don't understand why PE exists.. Can someone explain to me? Thanks!