a marble block of mass $2 \mathrm{kg}$ lying on the ice when given a velocity of  $6 \mathrm{m} {\mathrm{s}}^{-1}$ is stopped by frictional force in $10 \mathrm{s}$. Then the coefficient of friction is 
(take $\mathrm{g}=10 \mathrm{m} {\mathrm{s}}^{-2}$)