Answers by visitors named: Peter Pan

by the way, this is a brain teaser lol

Thank you

Using conservation of energy Efinal=Einitial + Work Neglecting rest mass energies Uf+Kf=Ui+Ki+W Starting and ending at rest so Kf=Ki=0 Therefore W=Uf-Ui Using Gravitational potential energy U=-Gm1m2/r When r is very large Uf=0 So W=Gm1m2/r