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Homework Help: Order of magnitude problem involving the force of repulsion between two persons

  1. Aug 27, 2012 #1
    1. The problem statement, all variables and given/known data

    ruZ5R.png

    2. Relevant equations

    [itex]\vec{F}[/itex] = k[itex]\stackrel{q1q2}{r^{2}}[/itex]

    3. The attempt at a solution

    6.022e23*(0.505) = 3.041e23C <-- electrons
    6.022e23*(0.495) = 2.981e23C <-- protons
    3.041e23 - 2.981e23 = 6e21C <-- the difference between the two charges
    [itex]\vec{F}[/itex][itex]_{e}[/itex] = (9e9Nm[itex]^{2}[/itex]/C[itex]^{2}[/itex])(6e21C)[itex]^{2}[/itex] / 2.25m[itex]^{2}[/itex]
    [itex]\vec{F}[/itex][itex]_{e}[/itex] = 1.44e53 N
     
  2. jcsd
  3. Aug 27, 2012 #2

    CAF123

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    Gold Member

    Re: Order of magnitude problem involving the force of repulsion between two persons..

    Given that the force of repulsion is similar to the gravitational force exerted on an object with a mass the size of earth, you should expect F ~ 1025N.

    There is an identical thread here:
    https://www.physicsforums.com/showthread.php?t=431698
     
  4. Aug 27, 2012 #3
    Re: Order of magnitude problem involving the force of repulsion between two persons..

    The answer gives me this error: "Your response is within 10% of the correct value. This may be due to roundoff error, or you could have a mistake in your calculation. Carry out all intermediate results to at least four-digit accuracy to minimize roundoff error."
     
  5. Aug 27, 2012 #4
    Re: Order of magnitude problem involving the force of repulsion between two persons..

    What is the answer that you put in the box?
     
  6. Aug 27, 2012 #5
    Re: Order of magnitude problem involving the force of repulsion between two persons..

    I put in F~10 25N.
     
  7. Aug 28, 2012 #6
    Re: Order of magnitude problem involving the force of repulsion between two persons..

    How do you get the number of protons?
     
  8. Aug 28, 2012 #7
    Re: Order of magnitude problem involving the force of repulsion between two persons..

    I would consider trying to enter 26 in the box. Depending on how you estimate, you may get 10^26. And the "weight" of the Earth is also of the order 10^26 (6x10^25).
     
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