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Homework Help: Period of the sun

  1. Nov 14, 2004 #1
    Could someone help me start this problem. My mind it in the angular momentum mode and I am having trouble seeing where to start on this one. :confused:

    The sun's radius is 6.96E8m and it rotates with a period of 25.3d. Estimate the new period of rotation of the sun if it collapses with no loss of mass to become a neutron star of radius 5.5km. Give the result in seconds.

    Thank you very much!
     
  2. jcsd
  3. Nov 14, 2004 #2
    With the given radius you can find [tex]I_{initial}[/tex] and [tex]I_{final}[/tex]. With the given period, find out [tex]\omega_{initial}[/tex]. Then you use conservation of angular momentum to achieve your answer.
     
  4. Nov 14, 2004 #3
    as such...(you don't need the moments of inertia exactly because it maintains a spherical shape and same mass so those factor out)

    [tex](r_i)^2 \omega_i = (r_f)^2 \omega_f[/tex]
    [tex]\omega_f = \frac{(r_i)^2 \omega_i}{(r_f)^2}[/tex]
    [tex] T_{new} = \frac{2 \pi}{\omega_f} [/tex]

    follow complete done
     
  5. Nov 14, 2004 #4
    I calculated two different answers, both of which were to my dismay incorrect....but I am thinking that a conversion error might be the culprit. I am having trouble understanding what "a period of 25.3d" is -- as in, what does "d" stand for....should it be a time unit?
     
  6. Nov 14, 2004 #5
    in a period d=days
     
  7. Nov 14, 2004 #6
    THANK YOU THANK YOU THANK YOU!!! to everyone involved in helping with this problem!! :biggrin:
     
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