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Turntable Acceleration question

  1. Sep 17, 2008 #1
    1. The problem statement, all variables and given/known data
    A point on a rotating turntable 20.0 cm from the center accelerates from rest to a final
    speed of .700m/s in 1.75s. At t=1.25s, find the magnitude and direction of (a) the radial
    acceleration, (b) the tangential acceleration, and (c) the total acceleration at that point


    2. Relevant equations



    3. The attempt at a solution
    I get the speed by comparing the the speed at 1.75s to speed at 1.25. I get
    this to be .5m/s
    To find the radial acceleration at that point I do (.5m/s)2/.20m = 1.25m/s2
    Is the tangential acceleration at that point 1.25/1.25? Which is the radial/time?
    Kevin
     
  2. jcsd
  3. Sep 17, 2008 #2

    LowlyPion

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    The tangential acceleration at that point is the change in tangential velocity. That would be the same acceleration you used to determine that it was moving at .5m/s namely (.7m/s) /1.75s

    Presumably you know to sum the accelerations as vectors for the final answer..
     
  4. Sep 17, 2008 #3
    Thanks but that what I'm unsure of. I simply assumed that this is a constant acceleration
    and so by simple comparing taking 1.75/.7=1.25/x, I get .5 m/s
    Did I start that wrong?

    Kevin
     
  5. Sep 17, 2008 #4

    LowlyPion

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    You should expect that the acceleration is uniform, and that looked fine.

    They should have said if it were not.

    Good Luck.
     
  6. Sep 17, 2008 #5
    Is that tang acceleration correct by using the radial acceleration at that point/time?
    So that 1.25m/s2/ 1.25s = 1 m/s2 for tang?

    Thanks,
    Kevin
     
  7. Sep 17, 2008 #6

    LowlyPion

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    Oops the acceleration is inverted. It's .7/1.75. Sorry for swapping the two.
     
    Last edited: Sep 17, 2008
  8. Sep 17, 2008 #7

    LowlyPion

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    That means you have a forward acceleration of .7/1.75 = .4m/s2

    And your radial acceleration is 1.25m/s2 as you already found.

    The angle then is tan-1(.4/1.25) = 17.74 degrees (ratio of Opposite/adjacent with respect to forward of the radius.)

    The magnitude is the RSS of .4 and 1.25 .
     
  9. Sep 17, 2008 #8
    Thanks,
    That makes sense to me. Thanks for your time. I'm getting
    ready to go take my first exam.

    Take care,
    Kevin
     
  10. Sep 17, 2008 #9

    LowlyPion

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    Best of luck then.
     
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