This is correct. The motion of the people is relative to the Portal. It doesn't matter if the trolley is accelerating the Portal towards them or something is accelerating them towards the Portal. Therefore they accelerate out of the other side with some retained momentum. Technically it probably resembles something in between pictures A and B.

This reminds me of the experiment about whether an airplane could take off from a treadmill.

[–] hemko@lemmy.dbzer0.com 6 points 1 year ago (1 children)

Only if you assume the people will experience friction against the portal.

If they would accelerate to the speed of the train within the time it takes them to go through it, they'd experience very high pressure change against the due to one part of body accelerating faster than the other. This would cause the bodies to explode out the portal

[–] Natanael@slrpnk.net 1 points 1 year ago

Yes, as I noted elsewhere in the thread, the part of the body exiting the portal will experience inertia as it enters into the space outside the second portal and it will be forcefully pushed by the next part of the body heading into the first portal and thus imparting momentum to the parts ahead.

If this momentum has to be taken from anywhere its from the portal itself and by extension the train.