Energy at earth's surface=potential energy+kinetic energy=−GMmR+K.E
Energy at earth's surface=−GMmR+0=−GMmR
Energy at altitude of 2R=E=P.E+K.E.
E=−GMm3R+12m(GM3R)12×2
[As,orbitalvelocity=(GMR)12]
By taking the difference of energies, we get
E=−GMm6R−(−GMmR)
E=5GMm6R=56mgR As,GM=gR2