Consider a two particle system with particles having masses $m_1$ and $m_2$. If the first particle is pushed towards the centre of mass through a distance $d$, by what distance should the second particle be moved, so as to keep the centre of mass at the same position?\\
(1) $d$\\
(2) $\frac{m_2}{m_1}$ d\\
(3) $\frac{m_1}{m_1 + m_2} d$\\
(4) $\frac{m_1}{m_2} d$