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No Instantaneous Speed?

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  1. May 16, 2015 #1
    1. The problem statement, all variables and given/known data
    dkjqFyQ.png

    2. Relevant equations

    ##v = r \omega ##??

    3. The attempt at a solution
    The answer is 0...why?
     
  2. jcsd
  3. May 16, 2015 #2

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Because the "object is rolling without slipping". That means that any point on the objects circumfence that is in contact with the surface on which it is rolling does not move forward of backward on the surface.

    (Oh, and saying "the instantaneous speed is 0" is NOT the same as saying "there is no instantaneous speed"!)
     
  4. May 16, 2015 #3
    The speed of any point of the rolling body is the sum of its speed due to translational motion and its speed due to rotational motion.

    What is the translational speed of the point of contact of the rolling body?

    What is the rotational speed of the point of contact of the rolling body?
     
  5. May 16, 2015 #4
    Well, I now see that there isn't enough data in the problem to calculate the rotational speed of the point of contact. But, the key idea is that the translational speed and the rotational speed are equal and opposite, leading to a net force of zero.
     
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