Are questions about the realism of movies on-topic? Some recent examples:
We have a lot of off-topic exclusions that are relatively easy to define - news and current affairs, recommendations, and some that are slightly harder to apply evenly such as triviality.
To add to this list with exclusions based around relatively small categories like this I think is starting to become too difficult to apply, and will certainly become hard for new users to understand and conform to - it feels like we would be becoming too 'walled garden' about the site. So I do not think we should make these questions off topic.
Specifically the questions above - the first one was a terrible question as well as was taking for granted the time and efforts of users of this site. The second question might be better asked elsewhere, but it may be interesting for some people to ask and answer questions about the realism of technology or situations staged in a movie.
As I have said on several meta questions and comments - don't be afraid of using downvotes if you think a question is bad or particularly uninteresting. If you think that a question might get a better answer elsewhere - help the user with a comment.
Realism, to me, is one of those questions that can be either really good, or just not on-topic for M&TV, but maybe another SE.
This question about Tin Tin, for example, was originally here until it was decided that the question would be a better fit on physics. Originally, Skeptics.SE was considered, but since the question asked for scientific possibility of a fictional action/scene, it was sent over.
I think, in general, if the question asks for mere plausibility, it might be just fine for us, but that all depends on the wording. If it downright asks for scientific reasoning, then I think the migration should be considered. (Confirmed with their mods, they are allowed on Physics.SE)
Your examples, specifically; the first one was just a bad question. However, assuming it was actually good, we would have probably either ended up answering it the best we could, or toss it to a SE with better understanding.
The second one, I would say would be a bit easier to answer because one only has to think of monorails, car washes, among other things that move vehicles along a track. I don't see one close reason that would stand out for me greatly other than too easy perhaps because of those simple mechanisms for moving vehicles on a pre-determined path.
I do agree with @iandotkelly that we can't be way too nit-picky about every little nuance of topics. Down-votes are there for a reason. If there turns out to be a trend of down-votes and concern with a particular topic, then we should evaluate it.