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Universal law of gravitation(variables)

  1. Nov 2, 2009 #1
    1. The problem statement, all variables and given/known data
    A planet has twice the mass of earth, but both planets share the same acceleration of gravity. The radius of the new planet in terms of the radius R of earth is....?


    2. Relevant equations
    F=G(m1m2/r2), G being the universal gravitation constant


    3. The attempt at a solution
    i think you have to manipulate the equation in some way but i cant figure out what to do first.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Nov 2, 2009 #2
    From N's law, you have:

    [tex]
    G\frac{Mm}{r^2} = ma_g
    [/tex]

    Because Earth and planet have same acceleration of gravity => a_g(E) = a_g(P) => relationship between masses and radii => radius of planet.
     
  4. Nov 3, 2009 #3
    thanks, i understand now
     
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