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 gets embedded into the block and moves 20 m before coming to rest. The coefficient of friction between the block and the surface is _____ . (Given g=10 ms−2)
(1) 0.50
(2) 0.90
(3) 0.65
(4) 0.25