Displacement of Water Leaking in a Boxcar

[SilentBlade91]

Homework Statement

A boxcar of length 7.8 m and height 2.3 m is at rest on
frictionless rails. Inside the boxcar (whose mass when empty is
2900 kg) a tank containing 1400 kg of water is located at the
left end. The tank is 1 m long and 2.3 m tall. At some point
the walls of the tank start to leak, and the water fills the floor
of the boxcar uniformly. Assume that all the water stays in
the boxcar. What is the displacement of the boxcar 9 s after
the water has settled in the bottom of the car (take positive
displacement as being to the right)?

Homework Equations

??

The Attempt at a Solution

I know I don't have an attempt I am sorry, I really don't know what to do.

 

[Delphi51]

I was dumbstruck, too. In reality it wouldn't move, but with zero friction I suppose it would. The water moves to the right, so I suppose the car would move to the left. As a conservation of momentum problem, the car would gain some velocity while the water is moving, then lose it as the water stops. Very difficult to sort that out, though. My instinct is telling me that probably the center of mass doesn't change (no external force so it can't move). So your big picture is
center of mass before = center of mass after