Question

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

(a) 2.5R 

(b) 4.5R 

(c) 7.5R 

(d) 1.5R.

Answer 1

(c) : Let the spheres collide after time t, when the smaller sphere covered distance x₁ and bigger sphere covered distance x₂. The gravitational force acting between two spheres depends on the distance which is a variable quantity.