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Homework Help: What is the downward acceleration?

  1. Mar 23, 2008 #1
    A yoyo consists of aunfirom disk with a string wound around the rim. the upper end of the string is held fixed. the yoyo unwinds as it drops. what is the downward acceleration?

    I got the idea that Inertia*acceleration=force on the rim.
     
  2. jcsd
  3. Mar 23, 2008 #2

    Doc Al

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    Staff: Mentor

    Consider the forces acting on the disk and the torques they produce. Apply Newton's 2nd law to both translational and rotational motion.
     
  4. Mar 23, 2008 #3
    I got it ,F=(M+lc/(R^2))ac

    Mg=ac(M+(1/2MR^2)/(r^2)
    ac=g/(1+R^2/2r^2)

    just one more question, I can't figure out the accerlation of a slipping cylinder in a ramp.

    how to apply slipping force, I mean the kinetic frictional force>?
     
  5. Mar 23, 2008 #4

    Doc Al

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    Staff: Mentor

    If the yo-yo is just a uniform disk with the string wound around the rim, this answer can be simplified.

    Just add the friction force to the mix. It equals [itex]\mu N[/itex].
     
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