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Ratio of gravitational/repulsive electrostatic force

  1. Nov 28, 2009 #1
    1. The problem statement, all variables and given/known data
    Calculate the ratio of the magnitude of the attractive gravitational force to the repulsive electrostatic force between two protons.


    2. Relevant equations
    Mass of proton = M = m = 1.672e-27 kg
    g = 9.80665m/s2
    Q = q = 1.60219e−19 C
    k = 8.9875e9 N•m2/C2


    [tex]F_{Gravity}=g\frac{Mm}{r^{2}}[/tex]

    [tex]F_{electric}=k\frac{Qq}{r^{2}}[/tex]

    3. The attempt at a solution
    The radius [tex]r[/tex] is not given, so I attempted to find it algebraically by plugging in numbers, and I get:

    [tex]F_{gravity}=\frac{2.74m/s^{2}\cdot kg^{2}}{r^{2}}[/tex]

    I feel certain I am on the wrong track.
     
  2. jcsd
  3. Nov 28, 2009 #2

    Redbelly98

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    For Fgravity you should use G, not g. I.e., not 9.8 m/s2
     
  4. Nov 28, 2009 #3
    Thanks, I changed g to G, but I'm still not sure what to do after solving for r
     
  5. Nov 29, 2009 #4

    Redbelly98

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    Don't solve for r, just leave it in the form

    Fgravity = {your expression here}
    Then do the same for Felectric.
     
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