Explain why it is not possible to use the equation ∆ Ep = mgh when determining the change in the gravitational potential energy of a satellite as it moves between orbits. I have concluded that GPE, ∆ u= mgh only if g is constant over the distance can anyone expand on this statement?

Question

anonymous · Answer

The change in the potential energy of the satellite-earth system is equal to the work done by the external force in quasi-statically bringing the system to the final configuration from the initial. Now, when we lift or lower an object, the change in potential energy of the system is mgh, only near the earth's surface, where the force of the earth on the object by the earth is constant (mg). However, when we deal with objects at a significant height above the earth, such as satellites, we cannot assume the force to be constant, since the accceleration due to gravity changes with height. Hence we cannot use the expression mgh.