From Mechanics

\displaystyle \mathbf{u}=\text{ 4}u\mathbf{i},\quad \mathbf{v}=\text{ 2}u\mathbf{j},\quad I=kmu

\displaystyle \begin{align} & \mathbf{I}=m\mathbf{v}-m\mathbf{u} \\ & =m(2u\mathbf{j})-m(4u\mathbf{i}) \\ & =-4mu\mathbf{i}+2mu\mathbf{j} \\ & kmu=\sqrt{{{(-4mu)}^{2}}+{{(2mu)}^{2}}} \\ & kmu=\sqrt{20{{m}^{2}}{{u}^{2}}} \\ & kmu=mu\sqrt{20} \\ & k=\sqrt{20}=2\sqrt{5} \end{align}