A 4.00-g bullet, traveling horizontally with a velocity of magnitude 400 m/s, is fired into a wooden block with mass 0.800 kg, initially at rest on a level surface. The bullet passes through the block and emerges with its speed reduced to 120 m/s. The block slides a distance of 45.0 cm along the surface from its initial position.
(a) What is the coefficient of kinetic friction between block and surface?
(b) What is the decrease in kinetic energy of the bullet?
(c) What is the kinetic energy of the block at the instant after the bullet passes through it?