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Homework Help: Am I doing this right?

  1. Sep 20, 2007 #1
    In outer space a rock of mass 3 kg is attached to a long spring and swung at constant speed in a circle of radius 7.5 m. The spring exerts a force of constant magnitude 640 N. What is the speed of the rock?

    I thought i was doing this right...but I guess not

    Fspring = Fcent.

    Fcent = m* v^2/r so.... v = sqrt(F*r/m)

    v = sqrt(640*7.5/3 ) = 41 m/s

    If anyone could tell me what I'm doing wrong, that would be alot of help!!! thanks! :-)
  2. jcsd
  3. Sep 20, 2007 #2

    Doc Al

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    Staff: Mentor

    Your method is fine. Just redo that calculation. (You're not off by much!)
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