Problem: A bullet of mass 0.018 kg and initial speed 300 m/s penetrates an initially stationary pop can of mass 0.055 kg and emerges with a speed 200 m/s. A) What is the initial momentum of the bullet and pop can system? I found this answer by 0.018 * 300 = 5.6 B) What is the final momentum of the bullet? I found this answer by 0.018 * 200 = 3.6 C) How fast is the can moving after the bullet emerges? I found this answer by 0.018(300-200) and then took that quantity and divided it by 0.055 = 32.73 m/s D) How much kinetic energy was lost (to heat, sound, deformation of can and bullet,...) in the process? Give your answer as a positive number. Here is my problem. I don't know how to obtain this. I thought that maybe I could calculate it by KE1 + KE2 = KE1 + KE2 where the left side of the equation is before the collision and the right side is after. Then when I add the right side, it is a little off from the left, so I thought that was the KE lost. However, the online program I'm using says it isn't. What am I doing wrong or how can I go about achieving this?