Two spherical bodies of mass M and 5 M and radii R and 2R respectively are released in free space with initial separation between their centers equal to 12 R. If they affact each other due to gravitational force only, then the distance covered by the smaller body just before collision is

The gravitational force between two spheres depends on their masses and the distance between their centers. The smaller sphere experiences a force due to the gravitational attraction of the larger sphere, which results in acceleration. The acceleration of the smaller sphere is calculated by dividing the gravitational force by its mass.
Similarly, the larger sphere also experiences acceleration due to the gravitational force exerted by the smaller sphere. However, since the larger sphere has a greater mass, its acceleration is proportionally smaller. The relationship between the force, mass, and acceleration illustrates the mutual interaction governed by Newton’s law of gravitation.

Gravitational force between the two spheres,
F = (GM x 5 M)/(12 R – x)²
Acceleration of smaller body,
a₁ = F/M = (G x 5 M)/(12 R – x)²
Acceleration of larger body,
a₂ = F/5 M = GM/(12 R – x)²