A Close Examination on Inelastic Collision

This paper examines the details of an inelastic collision when a bullet shoots a block vertically upward from below. With the assumption of constant interaction force between them, we obtain quantities of interest including the displacement for the block at the end of collision, the collision time, and in particular, the bullet's depth inside the block, which are not studied under the traditional assumption of very short collision time. We identify the condition under which the collision time can indeed be considered as negligibly short. The theory is applied to a well-known demonstration. Using the data extracted from photos of the demonstration, we calculate the magnitude of interaction force and the collision time, which can in no way be easily measured otherwise.