A particle having charge $10^{-9} \mathrm{C}$ moving in $x-y$ plane in fields of $0.4 \hat{j} \mathrm{~N} / \mathrm{C}$ and $4 \times 10^{-3} \hat{k} \mathrm{~T}$ experiences a force of $(4 \hat{i}+2 \hat{j}) \times 10^{-10} \mathrm{~N}$. The velocity of the particle at that instant is $\_\_\_\_$ $\mathrm{m} / \mathrm{s}$.