Identical point charges of +1.1 ¦ÌC are fixed to three of the four corners of a square. What is the magnitude q of the negative point charge that must be fixed to the fourth corner, so that the charge at the diagonally opposite corner experiences a net force of zero?

Answer 1

call side of square = 1

look at components along diagonal

2(1.1 *1.1 /1^2)cos 45 = 1.1 q/(sqrt2)^2

cos 45 = 1/sqrt 2

2(1.1) = q/sqrt 2

q = 2.2 sqrt 2