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Galaxy problems

  1. May 4, 2004 #1
    Our solar system is in the milky way galaxy. if you are told that in another galaxy a planet p has a circular orbit equal to that of the earth's (that is they both have the same radius). the masses of the suns in the 2 galaxys are Se and Sp respectively and planet p completes its orbit in half the time it takes the earth.

    How do i show that the mass of the sun in the earths orbit is 4 times the mass of the sun in planet p's orbit?
  2. jcsd
  3. May 4, 2004 #2


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    What is the relationship between the period of a planet's orbit around its "Sun", the mass of the star, the radius of the orbit, and any other factors that may be relevant?

    Have you learned of Kepler, the work he did, and what Newton subsequently showed concerning Kepler's results?
  4. May 4, 2004 #3
    Last edited: May 4, 2004
  5. May 4, 2004 #4


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    I meant, in general ... e.g. Earth, Venus, Jupiter ... Have you studied Kepler or Newton in class yet?
  6. May 4, 2004 #5
    we just studiend like F = (m1 x m2 x G)/r^2 and the relationship between g (acceleration due to gravity) and G (gravitational constant)
  7. May 4, 2004 #6
    i would think that you would need to have an understanding of keplars laws. More specifically, you need to have knowledge of a relationship between the period and the distance.
  8. May 5, 2004 #7
    thanx guys i figured it out using keeplers 3rd law.
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