WitCH 71: Plane Wrong

Here is another from the 2019 Specialist Exam 2, also courtesy of student PURJ. Again, we’ll semi-update from the examination report once people have had a chance to ponder and to comment.

UPDATE (01/11/21)

We shouldn’t have made this one so much of a hunt. The big problem is (c)(i), which is poorly worded, and for which the examination report gives the (notably casual) solution

    \[\color{blue}\boldsymbol{\theta < \sin^{-1}\!\left(\frac{m_2}{m_1}\right)}\]

This solution, however, makes no sense if \boldsymbol{m_2 > m_1}, in which case the mass will fall to the floor no matter the value of \boldsymbol{\theta}.

2 Replies to “WitCH 71: Plane Wrong”

  1. In part a, tension is not acting on the system, it is an internal affair of the system.

    Unlike in part b, in part c m2 may be greater than m1. Consequently the answer provided would be undefined.
    Is there anything else?

    1. Thanks, Banacek. Yes, the big problem is (c), where the report’s answer is simply incomplete. There’s some more clumsy wording, but (c) is the issue. I’ll update soon.

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