Question

two identical spheres of radius R are placed in contact .prove that gravitational force between them is directly proportional to forth power of radius of sphere (F directly proportional to R^4)

Answer 1

gravitational force between them
F = GMM'/R^2
= G M^2/(2R^2)
= G M ^2/ 4 R^2
Force is directly proportional to 1/4 R^2