1. The problem statement, all variables and given/known data Consider a system of a ball and the Earth. The ball is held at rest at an initial height, then dropped. Derive an expression for the net external work by external forces on BE. 2. Relevant equations W = Fx W = deltaK V = mgh K = (1/2)mv^2 3. The attempt at a solution My confusion from this arises from the following: there are no external forces on the system. Therefore, the net external work of the system should be zero. However, the kinetic energy of the system changes and the potential energy decreases. Because the kinetic energy of the system increases, there should be work done because of W=deltaK. Clearly I'm guilty of a logical fallacy somewhere along the lines, but I'm unsure where.