From Mechanics

Using

\displaystyle {{m}_{A}}{{v}_{A}}+{{m}_{B}}{{v}_{B}}={{m}_{A}}{{u}_{A}}+{{m}_{B}}{{u}_{B}}

Assume the 2 kg particle is moving in the positive direction,

\displaystyle \begin{align} & 2\times 5+3\times (-6)=2\times (-2)+3v \\ & 10-12=-4+3v \\ & 2=3v \\ & v=\frac{2}{3}\text{ m}{{\text{s}}^{\text{-1}}} \\ \end{align}

The 3 kg particle moves in the opposite direction to its original velocity.