Centre of Mass of Discrete Particles question from NEET 1997 (AIPMT)

Answer: (d)

1. $\vec{r}_{cm} = \frac{\sum m_i \vec{r}_i}{\sum m_i}$ depends only on the masses and their positions (hence on relative distances).
2. Forces change the motion of the centre of mass, not its location for a given arrangement.
3. So the answer is (d) forces acting on the particles.