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Homework Help: Calculate the angular momentum of a solid uniform sphere

  1. Nov 11, 2009 #1
    1. The problem statement, all variables and given/known data
    Calculate the angular momentum of a solid uniform sphere with a radius of 0.120m and a mass of 14.0kg if it is rotating at 6.00rad/s about an axis through its center.

    2. Relevant equations
    Angular Momentum = I * w
    I = mass*radius2/2
    w = 6.00rad/s

    3. The attempt at a solution
    When using the formulas above i am obtaining the answer 0.1008 however, that is not the correct answer. Any Ideas?

    Edit: I also know that the answer needs to be in kg * m2/s
  2. jcsd
  3. Nov 11, 2009 #2
    always take a careful look at question and gather all the information and equations you know to solve this problem. Maybe you can change a little bit of equations or connect them together and you will get it.
    L = I*ω
    Plug values given:
    0.5mr²*ω = 0.5*14*.12²*6.00= ____ kg∙m^2/s
    And the answer is 0.6048.
    yup. looks good to me! hope this helps.
    And by the way, just guessing, do you also need to calculate the KE for that?
    Last edited: Nov 11, 2009
  4. Nov 11, 2009 #3
    Yup... I see what i did wrong... in every calculation i did i was thinking cylinder for I instead of sphere. Thank you. And yes I do have to find the KE which turns out to be 1.45J

    Thanks again for the help,
  5. Nov 11, 2009 #4
    Wait. I revised my answer because there were some error. Please refer to that. Sorry about that...
    [0.5mr²*ω = 0.5*14*.12²*6.00= ____ kg∙m^2/s
    And the answer is 0.6048.]
    This is right. I calculated 0.4 instead of 0.5
    And I am glad my answer was helpful. :) Have a nice day!
  6. Nov 11, 2009 #5

    Your first answer was correct because the moment of inertia for a sphere is 2/5mr2

    So you did it correctly, and thanks again ^_^
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