Physics - Center of Mass Question with Solution | TestHub

The position vector of the center of mass for a two-particle system is given by ${\vec{R}}_{CM}=\frac{m_1{\vec{r}}_1+m_2{\vec{r}}_2}{m_1+m_2}$.

This expression shows that ${\vec{R}}_{CM}$ is a linear combination of ${\vec{r}}_1$ and ${\vec{r}}_2$, which means it must lie on the line connecting the two particles (or on the line segment between them if both masses are positive). Thus, both A and R are true, and R correctly explains A.