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Homework Help: Fluid problem.

  1. Apr 13, 2008 #1
    my professor gave us this problem on the homework assignment about Fluid.

    Planet X is a sphere made entirely of the mythical metal exoferrum, which has density 2810 kg/m3. What is the period of orbit for a satellite in circular orbit just above the surface of Planet X? (That's right: I did not give you the mass or the radius of the planet!)


    i have no ideal which equation i should use.

    I dont know how to start this kind of problem ,please help!
     
  2. jcsd
  3. Apr 13, 2008 #2

    Shooting Star

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    Homework Helper

    This has got nothing to do with fluids, and you have shown no work.

    Could you have done it if r had been given?

    Assume that some value has been given to you for the radius r, and just see how far you can proceed using 'r' as a symbol (or a number, if you like). If you get stuck, we are here.
     
  4. Apr 13, 2008 #3
    using newton's law of gravity, T^2= (4π^2*r^3)/GM

    volume of sphere is V=4/3πr^3
    ρ=M/V

    put in newton's law of gravity, T^2=3πV/GM T^2=3π/Gρ
     
  5. Apr 13, 2008 #4
    thanks a lot, the hint you gave is so helpful. i got it right.
     
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