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I need help with rotational kinetic energy problems

  1. Mar 10, 2015 #1
    B9aoQgo.png


    I tried to use this formula: KE=(1/2)(I)(w)^2, and work=change in KE


    For the first question, i tried to plug the number into the rotation kinetic energy formula:
    3600rpm=376.8rad/s
    (0.5)(2,000kg)(0.125m)^2(376.8rad/s)^2
    I found out this was the answer 1.1 x 106 J, but I got 2218410J

    For the second one, I did:
    (0.5)(7kg)(0.109)^2((6m/s)/(0.1m))^2
    And I got 21j, pretty sure is wrong.

    Can someone please help me out, or give me a hint??
    Really struggling.
    Does the change in kinetic energy equal to work?
     
    Last edited by a moderator: Mar 10, 2015
  2. jcsd
  3. Mar 10, 2015 #2

    haruspex

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    I get about the same.
    What's the formula for the MoI of a solid uniform sphere?
     
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