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Tangential and Normal of a rotating mass

  1. Sep 30, 2016 #1
    1. The problem statement, all variables and given/known data
    14.76.PNG

    2. Relevant equations
    at = Rα
    an = V2/ R = Rω2

    Vt
    Vn =0
    3. The attempt at a solution
    I found at=0
    an=5.66 m/s
    vt=3.364
    vn=0


    So v = vt = 3.364 m/s

    Correct?
     
  2. jcsd
  3. Sep 30, 2016 #2

    haruspex

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    If you correct the units, yes.
    Please show how you got that.
     
  4. Sep 30, 2016 #3
    oh yes, a in m/s^2 typo :)

    for vt, first, I need ω, which is found from an = v^2/R where R is L sinθ

    SO, v = sqrt (an*R) = sqrt (5.66*4sin30°) = 3.36 m/s
     
  5. Sep 30, 2016 #4

    gneill

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    What are the units associated with that 4 (highlighted in red)?
     
  6. Sep 30, 2016 #5
    4 in meter, which is the length of L
     
  7. Sep 30, 2016 #6
    the question is modified, it was shown 4 ft but actually it should be in meter.
     
  8. Sep 30, 2016 #7

    gneill

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    Ah. It would have been nice to have been made aware of this detail in the problem statement o_O

    In that case your tangential velocity looks okay.
     
  9. Sep 30, 2016 #8
    Hopefully I wouldn't make the same mistake next time, thanks for pointing out :)

    And at = 0 (rotating in constant angular speed), vn = 0 (constant radius R) correct?
     
  10. Sep 30, 2016 #9

    gneill

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    Yes.
     
  11. Sep 30, 2016 #10
    Great! Actually these questions appeared on my midterm today, and these were my answers
     
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