I need help with this problem. I dont know what equation to use. A 5.5g bullet is fired into a block of wood w/a mass of 22.6g. The wood block is initially at rest on a 1.5m tall post. After the collision, the wood block and bullet land 2.5m from the base of the post. What is the initial speed of the bullet? I tried to do this myself but all I got was the givens, I had no idea of where to start!