Question

Fine what happens to the gravitational force b/w two objects
(A) Distance b/w then doubled
(B)Masses of both the objects are doubled

Answer 1

Gravitational Force between two bodies of masses M and m separated by a distance d  = Fg = G M m / d²

Force is proportional inversely to the square of distance d between objects.

F = K / d² , where K is a constant
Originally,        F₁ = K/ d₁²     
when distance is doubled,   d₂ = 2*d₁ ==> F₂ = K/d₂² 

F₂ / F₁ = d₁² / d₂² = d₁² / 4d₁² = 1/4          So force becomes 1/4th.
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Force is proportional directly to the (product of) masses of the objects.
F = K M m       ,  K = a constant

F₂ / F₁ = K M₂ m₂ / K M₁ m₁  = 2 M₁ 2 m₁ / M₁ m₁ = 4 

So force becomes 4 times.