There have been numerous questions put on hold as showing "insufficient effort", generally in cases where the question has a simple, easily-found-out answer. But there are also a lot of questions that are marked as "duplicate" of other questions on Physics SE. Out of curiosity, can (note: not a request) duplicate questions be closed as showing "insufficient effort", especially if the question(s) they duplicate come up easily on a site search? That is, if one can easily answer the question by browsing through the site, does that question show "insufficient effort"?
I would argue that, yes a duplicate question would count as insufficient prior research. There is a search engine built into this site for a few reasons, one of which is to prevent duplicates. This site is also indexed favorably by Google (don't use others, so I cannot point to their efficacy), so searching that would should also bring searchers to this site.
However, I would also argue that it is irrelevant at that point because the question ought to be closed as a duplicate and not due to the homework aspect of "insufficient evidence."