A block of mass $5 \mathrm{~kg}$ is placed at rest on a table of rough surface. Now, if a force of $30 \mathrm{~N}$ is applied in the direction parallel to surface of the table, the block slides through a distance of $50 \mathrm{~m}$ in an interval of time $10 \mathrm{~s}$. Coefficient of kinetic friction is (given, $g=10 \mathrm{~ms}^{-2}$):