The measured height can be used to determine the velocity of the bullet. To calculate the veloicty of the bullet, we first need to determine the mass of the block and the bullet. The mass of the bullet is determined by weighting another bullet from the BB gun. The block has already been weighed (before suspension). The block's recoil distance is measured from the displacement of the slider on the meter stick. From this distance and the length of the strings supporting the pendulum one can determine the maximum height obtained by the block-bullet system. Conservation of energy is then used to obtain the velocity of the recoiling system. Conservation of momentum then allows one to calculate the velocity of the bullet.