A particle $A$ of charge $\mathrm{1 }\mathrm{\mu C}$ is held fixed at a point $\mathrm{P}$ in free space. Another particle $\mathrm{B}$ of same charge and mass $4 \mathrm{mg}$ is kept at a distance of $\mathrm{1 }\mathrm{mm}$ from $\mathrm{P}$. If $\mathrm{B}$ is released then its velocity at a distance of $\mathrm{9 }\mathrm{mm}$ from $\mathrm{P}$ is (Take $\frac{1}{4{\mathrm{\pi \epsilon }}_0}=9\times {10}^9 {\mathrm{Nm}}^2{\mathrm{C}}^{-2}$)