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Homework Help: Force on two particles?

  1. Aug 27, 2009 #1
    force on two particles??

    1. The problem statement, all variables and given/known data

    A charge q1 =4uC is at the origin, and a charge q2 = 6.0uC is on the x axis at x = 5m. In what follows, i denotes the unit vector in +x direction.

    i know how to do this problem, just plug into equation and go. but i keep getting the wrong answer. i will show what im doing and hopefully someone will see my mistake. might be something wrong with my constant or my conversion factor.

    2. Relevant equations

    this problem uses the whole F= k * ((q1q2)/r^2)

    q1 = 4uC i converted to C to get 4 x 10 ^ -6 C
    q2 = 6uC converted to C to get 6 x 10 ^ -6 C
    r = 5
    k = 1.3807 x 10 ^ -23

    3. The attempt at a solution

    just plug and chug

    1.3807 x 10 ^ -23 * 4 x 10 ^ -6 * 6 x 10 ^ -6 = 3.314 x 10 ^ -34

    divide by r^2 (25) = 1.325 e -35
    that is not right. should be a normal number not to a power

    any help would be great

  2. jcsd
  3. Aug 27, 2009 #2
    Re: force on two particles??

    Thats the issue with plug-and-chugging and not understanding what the formula is about... the value of 'k' that you are using is for the Boltzmann constant k, and not the constant of proportionality here implied by the 'k' here, which is actually = [tex]\frac{1}{4\pi\epsilon}[/tex]
  4. Aug 27, 2009 #3


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    Homework Helper

    Re: force on two particles??

    Yes, there's lot of constants that use "k" (k for constant): the Coloumb constant, the Boltzmann constant, the spring constant...
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