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Homework Help: Which radius (r or R) should you use? Why?

  1. Nov 12, 2008 #1
    1. The problem statement, all variables and given/known data
    A rolling wheel of radius r has translational velocity v as well as angular velocity w. Here you will relate translational velocity to angular velocity. Since the circumference of a circle of radius r is 2p r, every time the center of mass moves a distance 2p r, the object rotates a full circle (2p radians). If this happens in a time T then
    v = Dx/Dt = 2p r / T (1)
    and w = Dq/Dt = 2p/T (2)
    Combine these equations to find an expression for w in terms of v.

    2.When applying equation 1 (in question 1) to our system, which radius (r or R) should you use? Why?
    2. Relevant equations
    so i figured out the first question, i was just putting it up so you knew what was going on. But as far as equations i dont think there would be any for this question

    3. The attempt at a solution
    I think it should be r since in the equation and statment they only refer to r and not R
  2. jcsd
  3. Nov 12, 2008 #2


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    Gold Member

    Just divide the two equations and solve the resulting equation for w.
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