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Rotational Motion Problem

  1. Jul 29, 2017 #1

    gex

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    1. The problem statement, all variables and given/known data
    A uniform, spherical cloud of interstellar gas has mass 2.03×1030 kg and radius 1.03x1013m and is rotating with period 1.43×106 years. The cloud collapses to from a star 7.03x108m in radius. Find the star's rotation period.

    2. Relevant equations
    I1ω1=I2ω2
    Θ=ωt
    3. The attempt at a solution
    Determine ω:

    2π=ω(1.43×106)
    ω=4.4×10-6
    Use Moment of Inertia Equation: I=2/5(mr2)
    I1=8.61×1055
    I2=4.01×1047
    ∴ ω2=944.74 rad/year
    Determine t:
    Θ=ωt
    ∴ t=Θ/ω
    =2π/944.74
    =6.7×10-3
    =2.42 days

    Hey guys, I've been trying to do this homework question for a while now but I can't seem to get to the answer of 88.9 minutes. Any help getting there is much appreciated. Thank you all in advance.
     
  2. jcsd
  3. Jul 29, 2017 #2

    haruspex

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    I agree with your method and answer.
     
  4. Jul 29, 2017 #3

    gex

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    Wow odd. I will ask the teacher about the provided answer being incorrect then, thank you for shedding some light on this haruspex.
     
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