Answer
$8.33\times 10^{3}J$
Work Step by Step
By work-energy theorem,
Work done = Change in KE.
$W=\frac{1}{2}mv^{2}-\frac{1}{2}mu^{2}$
$m=\frac{2W}{v^{2}-u^{2}}=432kg$
Now, work done =$\frac{1}{2}mv^{2}-\frac{1}{2}mu^{2}=\frac{432}{2}((30\times\frac{1000}{3600})^{2}-(20\times\frac{1000}{3600})^{2})=8.33\times 10^{3}J$
