From Mechanics

\displaystyle m=\text{ 2}\text{ kg}, \displaystyle \quad \mathbf{u}=12\mathbf{i}\ \text{ m}{{\text{s}}^{-1}}, \displaystyle \quad \mathbf{v}=6\mathbf{j}\ \text{ m}{{\text{s}}^{-1}}

\displaystyle \begin{align} & \mathbf{I}=m\mathbf{v}-m\mathbf{u} \\ & =2(6\mathbf{j})-2\left( 12\mathbf{i} \right) \\ & =-24\mathbf{i}+12\mathbf{j} \\ & I=\sqrt{{{(-24)}^{2}}+{{12}^{2}}} \\ & =26\textrm{.}8\text{ Ns} \end{align}