Question

Three identical spheres each of radius R are placed such that their centres lie on a straight line. What is the location of their centre of mass from the centre of the first sphere?

(a) R

(b) 2R

(c) 3R

(d) 4R

I got this question at a job interview.

The doubt is from System of Particles topic in section System of Particles and Rotational Motion of Physics – Class 11

Answer 1

The correct answer is (b) 2R

To elaborate: Distance between first and last sphere = R + 2R + R = 4R

Since the spheres are identical and lie in a straight line, the centre of mass will lie exactly in the middle.

Hence the centre of mass lies at a distance of 2R from the centre of the first sphere.