# What is the magnitude and sign of q1 if the net force on q3 is zero?

Three-point charges are arranged on a line. Charge q3= +5.00 nC is at origin. Charge q2= -3.00 nC is at x= +4.00 cm. charge q1= is at x=+2.00 cm.

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- NCSLv 72 months agoFavourite answer
q1 must have opposite sign to q2 and so is positive.

Taking into account the push/pull of q1 and q2 on q3, and taking "right" as positive,

F = 0 = k * q3 * (q2 / (4.00cm)² - q1 / (2.00cm)²)

which is true when

q2 / 4² = q1 / 2²

Given magnitude q2 = 3.00 nC, then

q1 = ¼*3.00nC = 0.75 nC

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