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Calculate the magnitude of the total angular momentum of the woman

  1. Apr 3, 2009 #1
    Question:

    A woman with a mass of 55.0 is standing on the rim of a large disk that is rotating at an angular velocity of 0.550 about an axis through its center. The disk has a mass of 106 and a radius of 4.10 .


    a.)Calculate the magnitude of the total angular momentum of the woman-plus-disk system. (Assume that you can treat the woman as a point.)


    Here is my attempt.

    L = I(omega)
    = [(1/2)mr^2]omega
    = [(1/2)(106 kg + 55 kg)(4.10m)^2]*3.456 rad/s
    = 5143.8 kg m^2/s

    =4676.7 which is wrong anyone got any incite?
     
  2. jcsd
  3. Apr 3, 2009 #2

    rl.bhat

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    Calculate the moment of inertia of disc and woman separately and then add.
     
    Last edited: Apr 3, 2009
  4. Apr 3, 2009 #3
    so i am going to use the formula

    I = R^2 * M

    and do

    I = 4.1^2*55 + 4.1^2*106?
    i got my answer as 5371.41

    is that correct?


    i get one chance to get it right so just making sure
     
  5. Apr 3, 2009 #4

    rl.bhat

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    What is I for disc?
     
  6. Apr 3, 2009 #5
    It is:

    I = (m*r^2)/2

    so it would then be

    I= (55*4.1^2)/2 + (106*41.^2)/2
    =1353.21

    Is that right?
     
  7. Apr 3, 2009 #6

    rl.bhat

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    No. What is I of woman?
     
    Last edited: Apr 3, 2009
  8. Apr 3, 2009 #7
    I = R^2 * M?

    so then add those two together for

    I=4.1^2* 55 +4.1^2*106*(1/2)
    =1815.48?
     
  9. Apr 3, 2009 #8

    rl.bhat

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    That is right.
     
  10. Apr 3, 2009 #9
    well the answer was wrong.

    It was 6270

    however i would like to know how this answer came to be
     
  11. Apr 3, 2009 #10

    rl.bhat

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    In your problem angular velocity is 0,550 ?. What is the unit?= [(1/2)(106 kg + 55 kg)(4.10m)^2]*3.456 rad/s
    = 5143.8 kg m^2/s

    =4676.7
    which is wrong anyone got any incite?
    From where did you get 3.456?
    Why the two answer are different?
     
  12. Apr 3, 2009 #11
    How many women are you going to incite?
     
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