  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.
