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Homework Help: Torque problem involving rolling disk stopped by a force

  1. Nov 9, 2008 #1
    A potter has a stone disk of radius 0.483 m and mass 101 kg rotating at 71.9 rev/min. The potter stops the wheel in 6.54 seconds by applying a wet towel against the rim with a radially inward force of 103 N. Find the effective coefficient of kinetic friction between the whell and the wet towel.
    my work
    angular velocity= 71.9 x 2 x pi /60seconds=7.53
    alpha =7.53 / 6.54=1.15
    Torque=alpha x I = 1.15 x (101) x (.483^2) =27.13 N-M
    27.13 = torque = F r sin 90
    F =27.13/ (0.483)
    F =56.17 Newtons = Frictional force
    56.2 = u Fn
    u=56.2 / (103) ----> 103 is given as the radially inward force, Fn
    u=.545

    why is this wrong? does anyone know why? thanks
     
  2. jcsd
  3. Nov 10, 2008 #2

    tiny-tim

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