From Mechanics

\displaystyle m=\text{ 12}00\ \text{kg}, \quad u=\text{ 8}\ \text{m}{{\text{s}}^{-1}}, \quad v=\text{ }0\ \text{m}{{\text{s}}^{-1}}

\displaystyle \begin{align} & I=mv-mu \\ & =1200\times 0-1200\times 8 \\ & =-9600\text{ Ns} \end{align}

Magnitude of Impulse = 9600 Ns