During a certain war, millions of shells were fired by country A towards the west, and even more shells were fired back by country B towards the east. The average momentum of each bullet were the same on average. What was the ultimate effect on the angular momentum of Earth?
Here's my try: B fired more bullets than A. Because average momentum of each bullet is the same, there must be a net change in momentum. As such the Earth's angular momentum would have to change.
However, the answer was that there was no effect, not even a very slight one. Why is that so?