$\mathrm{U}_{1}-\mathrm{U}_{2}=\Delta \mathrm{K}.$
$\mathrm{KQq}\left[\frac{1}{\mathrm{r}_{1}}-\frac{1}{\mathrm{r}_{2}}\right]=1 / 2 \mathrm{mv}^{2}-0$
$\mathrm{v}=\sqrt{\frac{2 \mathrm{k} \mathrm{Q} \mathrm{q}}{\mathrm{m}}\left[\frac{\mathrm{r}_{2}-\mathrm{r}_{1}}{\mathrm{r}_{1} \mathrm{r}_{2}}\right]}$
$=\sqrt{\frac{2 \times 9 \times 10^{9} \times 5 \times 10^{-6} \times 2 \times 10^{-6} \times 2.5}{0.1 \times 3 \times 0.5}}=1.73 \mathrm{\,m} / \mathrm{s}$



