A square 1 m on its side has charges on every corner. Calculate the electric field on the upper right corner of the square. Let the charge on each corner be 40 x10-9C.

Question

Do I use K(Q*4)/r^2=F
Then F/(Q*4)=E
K=8.99*10^9 Nm^2/C^2

Answer 1

No, no, no.

Forces are vectors, you have to add them as vectors.

You have the across the diagonal force (distance is not 1), and the two corner forces at 90 degrees to each other. If you analyse it you can eliminate all side directions, so (In my head) the force will be along the diagonal direction
F=kq^2(1/s^2)(sin45 + cos45+1/2)

where s is 1 m