A bullet is fired through a wooden board with a thickness of 11.0 cm. The bullet hits the board perpendicular to it, and with a speed of +390 m/s. The bullet then emerges on the other side of the board with a speed of +234 m/s. Assuming constant acceleration (rather, deceleration!) of the bullet while inside the wooden board, calculate the acceleration.
And Calculate also the total time the bullet is in contact with the board (in sec).