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Homework Help: Gravitational force between 2 particles

  1. Apr 2, 2008 #1
    1. The problem statement, all variables and given/known data

    A uniform, solid, 1900kg sphere has a radius of 5.00m. Find the gravitational force this sphere exerts on a 1.50kg point mass placed at the following distances from the center of the sphere: (a) 5.01m , and (b) 2.45m.

    2. Relevant equations

    Fg = GMm/r^2

    volume of sphere = (4/3)piR^3

    density of sphere = M/volume

    ratio of point mass to shere:

    M/msphere = (4/3piRM^3)/(4/3piRsphere^3)

    Mmass = msphere(Rmass/Rsphere)^3

    G(M)(mmass)/r^2 = Gmass(msphere(rmass/rsphere)^3)/Rsphere^2

    = G(mmass)(msphere)rmass/rsphere

    3. The attempt at a solution

    Fg = G(1900)(1.50)(5.01)/5^2 = 3.8x10^-7

    Fg = G(1900)(1.50)/5^2 = 8x10^-8

    nothing, I'm not sure what I'm doing wrong, any help is greatly appreciated.
  2. jcsd
  3. Apr 2, 2008 #2
    Where are the 5^2 coming from?
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