By conservation of momentum $\begin{aligned}& \mathrm{p}{\mathrm{i}}=\mathrm{p}{\mathrm{f}} \
& \mathrm{O}=\mathrm{m}1 \mathrm{u}{1+} \mathrm{m}_2 \mathrm{u}_2 \& \frac{\mathrm{u}_1}{\mathrm{u}_2}=-\left[\frac{1}{2}\right] \text { as } \frac{\mathrm{m}_1}{\mathrm{~m}_2}=\frac{2}{1}
\end{aligned}moveinoppositedirectionwithspeedratio1: 2$