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## Homework Statement

Given that we have q1 = -4nC on the y-axis at y=0.60m. q2 on the y-axis at y= -1.20m. What must be the sign and magnitude of q2 be for the net electric field at the origin to be:

a. Zero

b. 50 N/C

## Homework Equations

E=KQ/R

^{2}

## The Attempt at a Solution

I used: E

_{T}= E

_{1}+ E

_{2}

Since E

_{T}= 0 ; rearranging the equation: E

_{1}= - E

_{2}

Both K can be cancelled out leaving us with: Q

_{1}/ R

_{1}

^{2}= - Q

_{2}/ R

_{2}

^{2}

Then, Q

_{2}= - Q

_{1}(R

_{2}

^{2}) / R

_{1}

^{2}

Substituting the values: Q

_{2}= - (-4x10

^{-9})(1.20m)

^{2}/ (0.60m)

^{2}

Equals 1.6x10

^{-8}Coulombs, but in my test, my prof corrected and added negative sign on the answer. Am I doing something wrong?