Consider a 5-kg object interacting gravitationally with the earth. Imagine that we set up a standard reference frame with the z axis pointing vertically upward. If the interaction's potential energy when the object is at z = 5 m is -50 J, what is the approximate z-position of the object when it is at its reference separation from the earth?
What they mean by "reference separation" is that point where the potential energy is zero. The potential energy is of the form:
V(z) = mg z + c
where c is some constant which ...
A detailed solution is given.