Solve the all parts of given problem:
Problem: A bullet is fired with a speed of 800 m/s into a 10 cm thick block of wood. The block of wood remains stationary, while the bullet exits the other side of the block traveling at 200 m/s.
Part A: What was the average acceleration of the bullet while in the block of wood?
Part B: What is the minimum additional thickness of wood that would be needed to stop the bullet assuming the same acceleration as the bullet encountered in block?
I don't understand how to get the answer. Can you please help me with this problem?