The gravitational force F between the two bodies of masses M and m is kept at a distance d from each other such that:;
F = G (m1.m2/r2)
Where,
m1 and m2 are the masses of the two bodies.
G is the gravitational constant.
r is the distance between the two bodies.
Given that the distance is reduced to half then,
r = 1/2 r
While the force between the two bodies is inversely proportional to the square of the distance between them which is given as:
F = G (m1.m2/(r/2)2)
F= 4G m1.m2/ r2
Therefore, when the distance is halved, the gravitational between these two bodies becomes four times