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Please help circular motion

  1. Nov 14, 2008 #1
    Please help!! circular motion

    1. The problem statement, all variables and given/known data

    At what height above teh earths surface would a satellite have to orbit in order that it be stationary in reference to a point on the earth? b. what would be it's speed? c. How would you describe the general location of that point in relation to the earth's surface?

    2. Relevant equations

    Fg= (G)(M1M2)
    r2
    G=6.67x10-11Nm2/kg2
    Fw=Mg
    Fc=M v2
    r
    a=v2
    r
    Earth mass=6x1024kg
    Earth radius=6.4x106m

    3. The attempt at a solution

    Can someone help me and let me know where to start? I know how to find the velocity, but seems like i dont have enough information? is there something i'm missing?? please help!!!
     
  2. jcsd
  3. Nov 14, 2008 #2

    Redbelly98

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    Re: Please help!! circular motion

    The whole key to this problem is to think what the orbital period would be, if the object is to be "stationary in reference to a point on the earth".

    That, plus an equation relating the orbital period to v and r.
     
  4. Nov 14, 2008 #3
    Re: Please help!! circular motion

    thanks for the clue.....but is it a day??
     
  5. Nov 14, 2008 #4

    Redbelly98

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    Re: Please help!! circular motion

    Yes.
     
  6. Nov 14, 2008 #5
    Re: Please help!! circular motion

    thank you thank you redbelly!!! now i can starting working on the problem!
    but one more question if you dont mind...after i get all the answr i get how would i describe the general location of that point in relation to the earth's surface?
    to be more clear, what is that question asking for?? again thank you for your help!!!! greatly appreciates it
     
  7. Nov 14, 2008 #6

    Redbelly98

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    Re: Please help!! circular motion

    The question is asking for the height or altitude of the satellite above the Earth's surface. In other words, the distance from the satellite to the surface directly below it.

    Note however that "r" in these equations is distance from the satellite to the center of the Earth.
     
  8. Nov 14, 2008 #7
    Re: Please help!! circular motion

    using period (T) as one day, which is 86400sec. In order to find "r" i used Fg=Fcp, which cancels out the mass of the shuttle:
    (6.67x10-11 Nm2/kg2)(6x1024kg/r2) = 4pie2/(86400s)2, after all the math is done i have r=4.23x107,so is this the height from earths surface and shuttle , or do i have to add or subtract that number from the earth's radius??
    if r is correct, v=3076.14 m/s
    What does this sentence mean?"How would you describe the general location of that point in relation to the earth's surface?"
    would i say like north,south, west, east, or what kind of answer is it asking for?
     
  9. Nov 14, 2008 #8

    Redbelly98

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    Re: Please help!! circular motion

    That's the distance from the satellite's orbit to the center of the Earth.

    I'm not sure. Does anybody else have an idea?
     
  10. Nov 14, 2008 #9
    Re: Please help!! circular motion

    Thank you Redbelly98 for answering my questions...I really appreciates your consistent help and patience. Thank you.
    At what height above the earths surface would a satellite have to orbit in order that it be stationary in reference to a point on the earth?
    So i would take r=4.23x10^7m and substract that from Earth radius=6.4x10^6m to get the height aboe the earths suface to the satellite right??
    sorry for keep bothering
     
  11. Nov 15, 2008 #10

    Redbelly98

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    Re: Please help!! circular motion

    Yes. (Assuming you really mean to subtract rEarth from r)
     
  12. Nov 15, 2008 #11
    Re: Please help!! circular motion

    yes, that's what i meant redbelly.....thank you thank you

    however, does anyone know What does this sentence mean?"How would you describe the general location of that point in relation to the earth's surface?"
    would i say like north,south, west, east, or what kind of answer is it asking for?
     
  13. Nov 17, 2008 #12

    Redbelly98

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    Re: Please help!! circular motion

    They might be asking about where such a satellite could be located. For example, it could not be located directly over the North or South pole, even if it's at the correct height. Do you see why?
     
  14. Nov 17, 2008 #13

    phz

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    Re: Please help!! circular motion

    Maybe they are searching for the term used to describe satellites that are kept stationary above the earths surface. There is a special word for this. It is a bit of a strange question if they mean it like that though, but that would be my guess.
     
  15. Nov 17, 2008 #14
    Re: Please help!! circular motion

    thank you thank you for all help!
    the answer was the a point above the equator.....

    Thank you all!
     
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