Question

what does the force of gravitation between two object when the distance between them is reduce to half. write the SI unit of energy

Answer 1

According to the Newton’s gravitational law, if the distant between two objects is reduced to half, assuming the objects either a puntiform masses or exacting spheres, the gravitational force’s numerical values become 4 times stronger because of the force dependent with the inverse of the square of the distant.
G → universal gravitational constant.

m1 → object 1’s mass.

m2 → object 2’s mass.

r→ the distance between the two object (in case they are approximated at puntiform objects) or the distance between the first object’s centre of mass and the second object’s centre of mass.

Attention: The Newton’s law may be use only either if the objects are approximated to puntiform or if their mass distribution is a spherical symmetry!