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Homework Help: Torque problem help!

  1. Nov 8, 2012 #1
    1. The problem statement, all variables and given/known data

    A wheel (M = 8.64 kg, R = radius 0.738 m) in the shape of a disk is rotating at fo = 76.6 rpm when a tool is pressed against the edge of the wheel, slowing it down at a constant rate to ff = 31 rpm in time t = 4.62 seconds. Find:

    τ, the magnitude of the torque exerted by the tool on the wheel

    2. Relevant equations

    Used the kinematic equations and the um.. torque formula.

    3. The attempt at a solution

    Here is my approach...

    ω_0 = 76.6 * 2π/60
    ω_f = 31 * 2π/60


    α = (ω_f - ω_0)/t

    So I believe I get...

    τ = Iα
    = mr²/2 * (ω_f - ω_0)/t
    = 8.64 * 0.738²/2 * (3.25 - 8.02)/4.62
    ≈ -2.43?
  2. jcsd
  3. Nov 8, 2012 #2


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    Homework Helper
    Gold Member
    2017 Award

    Looks good to me (if proper units are included in the answer). :smile:
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