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Homework Help: Linear Speed and Circular Motion Problem

  1. Oct 8, 2006 #1
    Ok, im having a hard time figuring this problem out for two reasons, the first is that my teacher is very tricky, 2nd is that I'm not sure how to work it out.

    An air puck is tied to a string and allowed to revolve in a circle with circumference if 2pi. The other end of the string passes through a hole in the center of the surface and a mass of 1kg is tied to it. If the suspended mass remains in equilibrium..
    A) What is the magnitude of the force that maintains the circular path
    B) What is the linear speed of the puck

    So, what I got out of this question is:
    2pi*r = cir... so r=1
    m = 1kg

    So, with the information given, we need to find Fc (force that maintains circular path). The equations i have to find this are:

    Fc = m*(vt^2) / r
    Fc = m*r*(w^2)
    (w meaning angular speed)

    So, for either equation i need to find w, or vt. The equations i have for these are:

    vt = r*w
    w = Delta Theta / Delta T

    So by moving from equation to equation I'm still missing 2 variables, I can't figure it out :grumpy:

    Any help is appreciated!
  2. jcsd
  3. Oct 8, 2006 #2


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    Homework Helper

    Use Newton III for A.
  4. Oct 8, 2006 #3
    ...? Newton's 3rd law...?
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