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Homework Help: Kinetic Energy of Rolling Motion

  1. Oct 18, 2007 #1
    1. The problem statement, all variables and given/known data
    A 12g CD with a radius of 7.0 cm rotates with an angular speed of 35 rad/s.
    What is its kinetic energy?


    2. Relevant equations



    3. The attempt at a solution
    I used K=(1/2)mv^2(1+I/mr^2)
    v=[tex]\omega[/tex]r=(35rad/s)(0.07m)=2.45m/s
    K=(1/2)(0.012kg)(2.45m/s)^2(1)=0.36

    And it's wrong. Am i using the right formula? What should I do
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 18, 2007 #2

    Doc Al

    User Avatar

    Staff: Mentor

    For rotational KE, use:
    [tex] {KE} = 1/2 I \omega^2[/tex]
     
  4. Oct 18, 2007 #3
    I used that too and i still got it wrong.
     
  5. Oct 18, 2007 #4
    Are you keeping track of units. If its not the problem, just show your calculation
     
  6. Oct 18, 2007 #5
    Oh I know what i did wrong now i forgot to multiply by 1/2. THanks for the help
     
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