The gravitational potential energy of a body of mass 'm' at the earth's surface āmgRe. Its gravitational potential energy at a height Re from the earth's surface will be (Here Re is the radius of the earth)
−12mgRe
△U=U2−U1=mgh1+hRe=mgRe1+ReRe=mgRe2
⇒U2−(−mgRe)=mgRe2⇒U2=−12mgRe