Two objects exert a gravitational force of 3 N on one another when they are 10 m apart. What would that forced be if the distance between the two objects were reduced to 5 m?

Gravitational force             F=r2Gm1m2

Case (i) :      Mass of one object is doubled   i.e    m1′=2m1

∴  F′=r2G(2m1)m2    ⟹F′=2F    

Thus gravitational force gets also doubled

Case (ii) :      Distance between the objects is doubled    i.e    r′=2r

 ∴  F′=(2r)2Gm1m2   ⟹F′=4F      

Thus gravitational force gets reduced by 4 times.

Distance between the objects is tripled    i.e    r′=3r

 ∴  F′=(3r)2Gm1m2   ⟹F′=9F      

Thus gravitational force gets reduced by 9 times.

Case 

less than one you can't create energy