4) A bullet is fired into a rectangular lump of clay that is 14.9 cm thick. The bullet travels through the clay,
with its motion perpendicular to the face of the rectangular lump. The initial speed of the bullet is
375 m/s, and when it busts through the other side of the clay, its speed is 185 m/s.
a) Find the average acceleration of the bullet as it passes through the board. (4 points)