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Homework Help: Circular Motion and Friction (PLEASE HELP )

  1. Feb 5, 2008 #1
    Circular Motion and Friction (PLEASE HELP!!!)

    1. The problem statement, all variables and given/known data
    The coefficient of friction between a certain brass block and a large revolving turntable is µ = 0.21. How far from the axis of rotation can the block be placed before it slides off the turntable if the turntable rotates at a constant rate of 33 1/3 rev/min (so that it requires time T = 60/33.33 seconds to complete one revolution) ?

    2. Relevant equations

    I think that µsN=4(pi^2)(mrf^2) should work, except I don't understand how to solve this sans any mass or other information.

    3. The attempt at a solution

    All I can get is that T=3.49 rad/s. I just don't understand how to do this problem!
  2. jcsd
  3. Feb 5, 2008 #2
    Since you are dealing with forces here, the first thing you want to do is draw a freebody diagram to account for all of the forces acting on the ring.

    Then decide what theory you wish to apply to solving the prolem. Do you have this done? As it will be easier for us to guide you if you do.
  4. Feb 5, 2008 #3
    So I got F=mews=mg. F also =m(v^2/r). Insert equation for v=(2pir)/t into quation for F, and then set the two F equations to be equal to each other, ultimately resulting in mewsg=((2pir)^2/T)/r. I simply cannot get the numbers to manipulate correctly and I keep getting wrong answers.
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