1. The problem statement, all variables and given/known data A water tanker on a railroad has a plug that is opened. The tanker is moving at 5.0m/s Will the tanker speed up when the water is being drained? 2. Relevant equations m1*v1 = m2*v2 3. The attempt at a solution My original thought was yes it will speed up But after looking at the answer it says that the water being drained is moving horizontally at 5.0m/s, so there is no change in momentum. So no change in speed. Why is there no change in momentum? Isn't m1 decreasing? Is it something to do with not being an isolated system?