1. Change in P.E. for a system of Earth and mass is given by,
∆U = GMm \((\frac{1}{r_i}-\frac{1}{r_f})\)
2. For gravitational force, point of zero potential energy is taken to be at r = ∞.
3. Hence, U(ri) = 0 at ri = ∞
Final point rf is the point where the potential energy of the system is to be determined.
4. At rf = r
![](https://www.sarthaks.com/?qa=blob&qa_blobid=15515174917823538448)
This is gravitational potential energy of the system of object of mass m and Earth of mass M having separation r (between their centres of mass).