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I saw this question yesterday.

OP found a way to solve it using conservation of energy, and wants to investigate how the acceleration can be calculated using forces and torques.

OP also posted their method of solution, but got a wrong answer.

I realized that OP did not take into account the acceleration due to rotation of the mass on the ring, and the expressions of the normal force and friction are wrong.

Can we reopen this question?

It seems that this is not a "do my homework" problem (OP already solved it using another method, and showed their work on another (more interesting) method), and it requires some careful thought.

If we reopen it, then of course, the answer should not solve the whole problem, but rather, point out the mistakes OP made (they need to properly consider the acceleration of the rotating mass in order to calculate the friction and the normal force).

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    $\begingroup$ Why would we reopen it? From your description, the answer is finding a mistake in the calculations presented by OP, which makes it a clear example of a "check my work" question. This question already once failed a reopen review. $\endgroup$
    – ACuriousMind Mod
    Jun 27 at 9:49
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    $\begingroup$ Well there is a bigger issue, the question is a dupe. However I can't undo my reopen vote. $\endgroup$
    – Buraian
    Jun 27 at 10:09
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    $\begingroup$ I did not know that this question is a duplicate. Now I too feel that it should be closed. $\endgroup$ Jun 27 at 10:13
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IMO the question should completely scrap the explicit mathematical work and asking for others to check it. If there really is a conceptual question, then it should be able to stand on its own. Putting in the work and asking others to check it (even with inserting the word "conceptual") makes it seem like a check-my-work question.

To be honest though, I'm not fully convinced this is a conceptual question. As the question is so far, the "concept" seems to be, "how can I write down the correct equations?" Of course, another user can pull relevant concepts from this, but the question isn't actually asking about them. And as a reminder, just because you see a concept to talk about does not mean that is what the post is actually asking about (It's a nice way to justify reopening almost any question though).

With that said, it seems like a borderline case. It looks like it will be reopened since there are 4 reopen votes currently despite a unanimous "leave closed" in the review (if one calls for a borderline question to be reopened in meta, chances are it will be reopened; there are many users who are fairly lenient on site policy and definitions therein), but I think I'll pass on making a judgement on this one without thinking more about it and looking into it further.

If we reopen it, then of course, the answer should not solve the whole problem, but rather, point out the mistakes OP made.

If this is what the answers need to be then indeed the question should remain closed.

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FWIW I have voted to reopen the question, but experience tells me the chances of reopening are very low. PSE moderators don’t like to admit to error.

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    $\begingroup$ What has "admitting error" to do with it? Questions are reopened when 5 users (or a moderator) vote to reopen it, regardless of who closed it. For this particular question, at least 3 other users agreed after the fact it should remain closed. $\endgroup$
    – ACuriousMind Mod
    Jun 27 at 9:56
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    $\begingroup$ For the record, at the time I reviewed it, I selected Leave Closed because the question was still focusing on what's wrong. However, since it has been edited quite substantially since then, I have voted to reopen. $\endgroup$ Jun 27 at 10:21

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