A bullet of mass 0.1 kg moving horizontally with speed 400 ms^-1 hits a wooden block of mass 3.9 kg kept on a horizontal rough surface. The bullet…

A bullet of mass $\displaystyle 0.1$ kg moving horizontally with speed $\displaystyle 400 \mathrm{~ms}^{-1}$ hits a wooden block of mass $\displaystyle 3.9$ kg kept on a horizontal rough surface. The bullet gets embedded into the block and moves $\displaystyle 20$ m before coming to rest. The coefficient of friction between the block and the surface is $\displaystyle \_\_\_\_$. (Given $\displaystyle \mathrm{g}=10 \mathrm{~m} / \mathrm{s}^2$ )