Just some thoughts on solving questions relating to forces, etc. How do I know when to use momentum to solve the problem or when to use conservation of energy in solving a problem? For example: A bullet travelling at 1000m/s strikes and pass through a 2kg block initially at rest from the bottom of the block. The bullet emerges from the top of the block with a speed of 400m/s. To what maximum height will the block rise above its initial position?