The minimum uncertainty in the speed of an electron in an one dimensional region of length $2 a_0$ (Where $\mathbf{a}_0=$ Bohr radius 52.9 pm ) is $\_\_\_\_$ $\mathrm{km} \mathrm{s}^{-1}$. (Given : Mass of electron $=9.1 \times 10^{-31} \mathrm{~kg}$, Planck's constant $\mathrm{h}=6.63 \times 10^{-34} \mathrm{Js}$ )