Gravitational potential energy on the earth surface Ui=R−GMm
Gravitational potential energy at a height h above the earth's surface Uf=−R+hGMm=−R+3RGMm=−4RGMm
Gain in gravitational potential energy
ΔU=Uf−Ui=−4RGMm+RGMm=4RGMm+4GMm=4R3GMm
Gravitational potential energy in terms of acceleration due to gravity is ΔU=43mgR
=43×1×10×64×105
=48MJ