Energy conservation during free-fall. Here, is the total energy of the mass: i.e., the sum of its kinetic and potential energies. Potential energy with respect to gravity is PE = mgh. When the object is dropped, thrown downward or projected upward, its kinetic energy becomes KE , along with a factor of the initial velocity. The sum of the PE and KE is the total energy, which is a constant. Equating the initial total energy with the final total energy, you can determine the final velocity of the object.