A 96.0-g wooden block is initially at rest on a rough horizontal surface when a 11.4-g bullet is fired horizontally into (but does not go through) it. After the impact, the block–bullet combination slides 6.5 m before coming to rest. If the coefficient of kinetic friction between block and surface is 0.750, determine the speed of the bullet immediately before impact.

Answer 1

work done by friction:
(M+m)g*mu*distance
KE after imact:
1/2 (M+m)*v^2

set them equal, solve for v just after impact. Now, use the conservation of momentum

(M+m)V=mV' solve for V', the speed before the impact.