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Problem osof uncoupling a train

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Problem os uncoupling a train

As a kid I have seen several movies, cartoon etc. in which usually one guy just uncouple (unplugs (?), dunno) the rest of a running train and then runs off with the locomotive at full speed and escapes. I just remembered that and find it ridiculous and I wondered, which kind of problems you would encounter by try doing that. However I can imagine a following situation: two train wagon have two overlapping pieces of iron with a hole and one big iron stick is put in, so that they are interlocked. If one wagon moves now, there other will be pulled as well.The wholes are on top of each other, so there is a difference in altitude between them. That might be important.
Removing it, for example by pulling it out, seems at first easy, as there is no force, which presses it downwards apart from it's own weight, which seems to be a minor problem. However I would also think, that you would have friction. I think, that the iron stick is not perpendicular to the ground, as it has the two wagons pull it. So the angle might be slightly oblique and so the force pulling on the stick would be not parallel to the ground, hence you could split the force into two perpendicular parts, one parallel to the ground and one perpendicular to the ground.
However I wonder, if it possible to ignore friction, but keep the resistance of materials, so that one doesn't sink into one another. Similar to super fluids liquids. So I assume pulling the iron out would be possible, if push it upwards from the downside. I also wonder how such an object with no friction behaves, if you apply a really strong force on it. I just try to imagine the whole situation and check my physical understanding of things. So feel free to correct me or add a thought.