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Homework Help: Angular speed of yo-yo

  1. May 16, 2008 #1
    This is the question i got
    A yo-yo has radius 8.00cm and mass 0.180kg with small hoop.
    The yo-yo is released at rest and after yo-yo
    descended 75.0cm calculater the angular speed of the rotating yo-yo
    and the speed of its center.
    I tried to use K=1/2Mv^2+1/2IW^2 but i got weird number....
    I have the answer but I need t know how to solve it...
    Just in case the answer for angular speed is 33.9rad/s and
    the speed of its center is 2.71m/s.
    I'm seriously fall into the deep~~~~ocean.
  2. jcsd
  3. May 16, 2008 #2


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    Don't forget about gravitational potential energy...
  4. May 16, 2008 #3


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    The given answer is right. What did you do wrong? You aren't giving us near enough information to tell. What did you use for I?
  5. May 17, 2008 #4
    I use MR^2 for I.........
  6. May 17, 2008 #5
    Wouldn't I be

    I = \frac{m r^2}{2}

    which is the one for a solid disk? Or are we considering the fact that the yo-yo is made up of two disks?
  7. May 17, 2008 #6


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    The clue refers to a hoop, so I think the do want you to use mr^2. You get the correct answer that way. But we still don't know enough to tell where cecico went wrong.
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