A bullet is fired through a board 10.0 cm thick in such a way that the bullet's line of motion is perpendicular to the face of the board. The initial speed of the bullet is 400 m/s and it emerges from the other side of the board with a speed of 300 m/s.
(a) Find the acceleration of the bullet as it passes through the board.
(b) Find the total time the bullet is in contact with the board.