A bullet, mass m, is fired from the left into a block, mass m, placed at rest on a horizontal frictionless table. The block is initially placed to the left of and against a light spring, initially uncompressed. the block does not move appreciably during the time the bullet comes to rest in the block. afterwards the bullet and block move a total distance x to the right before stopping momentarily. Is mechanical or momentum conserved in this system? How do I find initial speed of the bullet?