A bullet is fired through a board, 14.0 cm thick, with its line of motion perpendicular to the face of the board. If it enters with a speed of 450 m/s and emerges with a speed of 220 m/s, what is the bullet's acceleration as it passes through the board?
1) -500 km/s2
2) -550 km/s2
3) -360 km/s2
4) -520 km/s2
5) -275 km/s2
Answer: 2