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Swing and angular displacement

  1. Nov 28, 2017 #1
    hi, we are a few non-native English speaker physics teacher and we wrote some questions for an assessment book
    but we can't be sure about this two similar question.
    a) are they accurate for rules of English, are we use correct terms is there a necessary change?
    b) are they accurate for rules of physics and are the answers accurate?
    FIRST QUESTION

    1. The problem statement, all variables and given/known data

    A child on an playground swings through a total of 32°. If the displacement is equal on each side of the equilibrium position, what is the amplitude of this vibration?
    a) 8° b)32° c)16° d)64°
    2. Relevant equations
    none

    3. The attempt at a solution
    one of my colleague says the answer should 8° I think it should be 16°
    second

    SECOND QUESTION
    1. The problem statement, all variables and given/known data

    the amplitude of a simple pendulum is 0.17 rad. what is the angular displacement of this pendulum for one complete cycle?
    a)0.17 rad b)0.34 rad c) 0.51 rad d)0.68 rad
    2. Relevant equations
    none

    3. The attempt at a solution

    my colleague says the answer should 0.68 rad. I think it should be zero rad.
     
  2. jcsd
  3. Nov 28, 2017 #2

    CWatters

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    The English is ok. Might be better to say "after one complete cycle". Your answers are correct 16 and 0.

    The distance is 0.64 rads, the displacement is 0 rads.
     
  4. Nov 29, 2017 #3
    my colleague says there is no such a term as angular distance, so "angular displacement for one complete cycle" corresponds 4 times amplitude.
    Do you have any reference, a link or textbook that use these terms?
     
  5. Nov 29, 2017 #4

    haruspex

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    This is ambiguous. It might be counting multiple traverses of the same arc. Depending on what is intended, could clarify by specifying "in a single direction" or "in one complete cycle"...
    Which displacements? The maximum displacements from equilibrium or the initial and final displacements?
    Certainly not.
    "Displacement" always means net change, regardless of path taken. If your colleague does not like "angular distance" then some other term must be found which makes the meaning clear.
     
  6. Nov 29, 2017 #5

    CWatters

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    Normally we just use "angle" rather than angular distance. Angle can be greater than 2pi.
     
  7. Nov 29, 2017 #6

    haruspex

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    Yes, but in regard to wording a question for students I feel that in itself would not be clear enough.
     
  8. Dec 4, 2017 #7
    thank you guys for making it clear what are your suggestions and answers
     
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