Potential energy is the energy stored in an object because of its position or state and it is relative. Hence, it increases as we go to greater heights from the surface of the earth. We had assumed that the potential energy of an object of mass m, at a height h from the ground is mgh and on the ground it is zero. When h is small compared to the radius R of the earth, let g be constant and let us use the above formula (mgh). However, for h with larger values, the value of g decreases with increase in height (h). For an object placed at infinite distance from the earth, the value of g is zero and earth’s gravitational force does not act on the object. So it is more appropriate to assume the value of potential energy to be zero there. Thus, for smaller distances, i.e. Heights, the potential energy is less than zero, i.e. It is negative.
When an object is at a height h from the surface of the earth, its potential energy is -GMm/(R+h), with M and R as the earth’s mass and radius, respectively.
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