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A rectangle with Charges on Each Corner - Find Missing Charge?

  1. Oct 12, 2014 #1
    1. The problem statement, all variables and given/known data
    A charge is to be placed at the empty corner of a rectangle to make the net force at corner A point along the vertical direction. What charge (magnitude and algebraic sign) must be placed at the empty corner if the three charges have the same charge of +8.45 μC?


    2. Relevant equations
    F = kq1q1/r^2

    3. The attempt at a solution

    because we know that the net force on A is going to be in the vertical direction we know this is the resultant. Therefore i know the horizontal forces must cancel out..but isn't there only one existing horizontal force coming from the charge at the bottom right corner?

    F = (8.99x10^9)(8.45 x10^-6)^2/d^2
     

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    Last edited: Oct 12, 2014
  2. jcsd
  3. Oct 12, 2014 #2

    BvU

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    Hi nerd, and welcome to PF :-)

    Show us your attempt and only then we are allowed to help. Why ? See the guidelines
     
  4. Oct 12, 2014 #3
    Okay I added my attempt..but i seriously do not know where to go from this :(
     
    Last edited: Oct 12, 2014
  5. Oct 13, 2014 #4

    haruspex

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    You don't have to worry about forces as such, just think about the fields.
    Suppose you put a charge q at the fourth corner. What horizontal field will this give at A?
     
  6. Oct 13, 2014 #5

    BvU

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    I don't see an attempt, and it certainly doesn't look like your own work. Tell me about the forces at A due to the other two yellow bulbs. Magnitude, direction ?
     
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