Question

Increase in internal energy of a gas when a moving container is suddenly stopped

Answer 1

its vertical edges A and B. Assuming that it moves along BA ,after a certain time the edge A moves to A', B to B', and thus, the effective space for the molecules remains always unchanged. Now considering the force parameter in the problem, here the forcing agent is only the edge B colliding with the molecules in the vicinity(let vicinity be the region BC, C being sufficiently close to B) of B. Now, I argue that the impulsive force imparted by B on the molecules near it, modifies the initial random motion direction of these nearby molecules, and forces them to move along BAdirection. But after BC, i.e. in the region CA, the molecules don't attain a perfectly horizontal motion, and the alignment along BA deteriorates as one moves from B to A, in a disciplined manner, and yet not changing the Maxwellian distribution. I consider layers within the container, at the not-so-clearly defined C junction, there's a continuous yet slightly increasing variation from BA direction, although the resultant velocity of these molecules may be in NW/SW directions. These molecules collide with those in the next layer, and these latter molecules undergo further variation from BA (not to forget that in all these layers, some molecules might even move in NE/SE/E(AB) directions, the fraction of which is relatively low, but increases, and becomes relatively higher while moving along BA). Thus this variation considerably increases in the vicinity of the A edge, and as such, magnitudes of the velocities of these molecules eventually re-organize themselves (due to the changing angle-factor at each layer of molecules) in such a way that the final energy-distribution curve varies too little from the initial one, to be of any significance at a practical level, whence the temperature

Answer 2

Actually if the temperature and pressure are constant then the moving train has no effect. Because there will be no change in temperature.

It can be different case if we say that the train is accelerating because then the velocity has to change. So we might consider a pseudo force for gas molecules. Now we now if there is force and gas molecules are moving so some work is done and energy is spent. So in this case the temperature will change and so internal energy has to change.