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

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1. Oct 12, 2014

### NerdingOut

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. Oct 12, 2014

### BvU

Hi nerd, and welcome to PF :-)

Show us your attempt and only then we are allowed to help. Why ? See the guidelines

3. Oct 12, 2014

### NerdingOut

Okay I added my attempt..but i seriously do not know where to go from this :(

Last edited: Oct 12, 2014
4. Oct 13, 2014

### haruspex

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?

5. Oct 13, 2014

### BvU

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 ?