Answer
$1.03\times 10^{7}$ $m/s$
Work Step by Step
The relation between kinetic energy $(K)$ and speed $(v)$ of an electron is expressed by the expression
$K=\frac{1}{2}mv^{2}$, in which $m$ is the mass of an electron.
or, $v=\sqrt {\frac{2K}{m}}$
Putting the given values, $v=\sqrt {\frac{2\times 300\times 1.6 \times 10^{-19}}{9.1\times 10^{-31}}}$ $m/s$
$v\approx 1.03\times 10^{7}$ $m/s$
$\therefore$ The speed the electron is $1.03\times 10^{7}$ $m/s$
