Initially the block is not moving with respect to ground while plank is moving, it means, relative motion is there between the plank and block due to which friction (kinetic) starts acting. Initial velocity of block is zero and final velocity is $\mathrm{10 }\mathrm{m}/\mathrm{s}$ and let $s$ is the distance travelled by the block over the ground, then:-

$\frac{m{\left(10\right)}^2}{2}-\frac{m{\left(0\right)}^2}{2}=0.2\times m\times 10\times s$
$$\begin{gathered} \Rightarrow 50=2s \\ \Rightarrow s=25\mathrm{ }\mathrm{m} \end{gathered}$$