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