A 580 kg cannon and a supply of 41 cannon balls, each with a mass of 38.9 kg, are inside a sealed railroad car with a mass of 31000 kg and a length of 53 m. The cannon fires to the right; the car recoils to the left. The cannon balls remain in the car after hitting the wall. After all the cannon balls have been fired, what is the greatest distance the car can have moved from its original position?

Answer 1

As I read this, the cannon balls remain in the car after shooting.

Well, the center of gravity will remain the same, so my immediate question is where were the cannon balls at the beginning, and at the end? If the same position, the car does not move.