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Homework Help: Air Puck Correct Method or not

  1. Jul 16, 2007 #1
    Air Puck !!! Correct Method or not...

    1. The problem statement, all variables and given/known data

    An air puck of mass 0.25kg is tied to a string and allowed to revolve in a circle of radius 1.0m on a frictionless horizontal table. The other end of the string passes through a hole in the center of the table and a mass of 1kg is tied to it. The suspended mass remains in equilibrium while the puck on the tabletop revolves

    a. What is the tension in the string ?
    b. What is the horizontal force acting on the string ?
    c. What is the speed of the puck ?

    2. Relevant equations

    [tex]\Sigma[/tex]F = m * a
    F_c = (m * v^2) / r
    a_c = v^2 / r

    3. The attempt at a solution

    [tex]\Sigma[/tex]F_y = m * a = 0
    T - mg = 0
    T = mg = 1.0kg * 9.8m/s^2 = 9.8N

    F_c = Tension on th string = 9.8N

    F_c = (m * v^2) / r = 9.8N
    (0.25kg * v^2) / 1.0m = 9.8N
    v = [tex]\sqrt{39.2}[/tex] = 6.3 m/s

    Is this correct......THANKS!!!
    Last edited: Jul 16, 2007
  2. jcsd
  3. Jul 17, 2007 #2


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    Homework Helper

    You seem to have it under control.
  4. Jul 17, 2007 #3
    3a. is correct, but it has incorrect --as near as I can tell- reasoning. Just recall Newton's Third Law for centripetal forces. Also, for 3b. it asks what is the horizontal force is; which requires an angle for the center of the system; not certain on how you are supposed to acquire that answer.
    Last edited: Jul 17, 2007
  5. Jul 17, 2007 #4
    Thanks a lot !!!
  6. Sep 24, 2007 #5
    very very helpful
    Last edited: Sep 24, 2007
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