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Homework Help: Finding the distance of 2 charges

  1. Feb 19, 2008 #1
    1. The problem statement, all variables and given/known data

    On attachment called Part B

    2. Relevant equations

    To get part A, I used a formula that I derived to be:

    square root [(2kq^2)/rm)] = v

    q =2.6 *10^-6 C
    k = 8.99*10^9 (Nm^2)/C^2
    r = 1.27m
    m = .0028 kg

    3. The attempt at a solution

    Now for part B it says to calculate the distance r when it is half of v, so I thought maybe I could rearrange the equation above to

    (2kq^2)/((v^2)*m) = r

    so it would look like...

    [2 * 8.99^9 * (2.6*10^-6)^2]/[((5.84/2)^2)*.0028] = r

    I used dimensional analysis and it comes out to be


    then I cancel what I can to get

    (Ns^2)/kg which in turn, becomes

    1ms^2/s^2 which at the end turns out to be left with only meters...

    So it seems like I'm right but obviously im not...

    OK in the attachment are the answers I submit after doing so many bizaarrreee calculations... ANy help would be appreciated... I think the reason I'm not getting hte correct answer is becuase the question states "at infinity" and I have no Idea what that means...

    Attached Files:

    Last edited: Feb 19, 2008
  2. jcsd
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