Answer
$v=1.4\times 10^{5} m/s$
Work Step by Step
By the conservation of energy;
Loss in energy = Gain in energy
Thus;
$q\Delta V=\frac{1}{2}mv^{2}$
$v=[\frac{2q\Delta V}{m}]^{1/2}$ [ Since, $\Delta V= Ed$]
$v=[\frac{2\times 1.6\times 10^{-19}\times 50, 000\times 2\times 10 ^{-3}}{1.67 \times 10^{-27} }]^{1/2}$
$v=1.4\times 10^{5} m/s$