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Homework Help: Lower inertia means it moves faster, right?

  1. Nov 13, 2012 #1
    I was working out a conceptual question that asks: if a disk and a hoop of equal mass and radius start from the top of a ramp, are realeased at the same time, and roll without slipping, which one reaches the bottom of the ramp first?

    Disk: I = 1/2(m)(r^2)

    Hoop: I = mr^2

    So the inertia of the disk ends up being lower. Lower inertia means the disk moves faster, right?
  2. jcsd
  3. Nov 13, 2012 #2


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    Gold Member

    "It accelerates faster" would be more correct. Looking at τ=Iα, for the the two cases with equal torque (τ) applied, if I (moment of inertia) was smaller, then α, (angular acceleration) would have to be larger.
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