Hi, thank you for posting your question here at Brainly.
To solve this problem, we use Coulomb's Law:
F = kQ1Q2/d^2, where k = 9x10^9
Q1 = 3.5 uC
Q2 = -3.5 uC
Q3 = 4.0 uC
But first, we find the distance between Q1 and Q3 and between Q2 and Q3.
d between Q1 and Q2:
d = sqrt[(0-0.4)^2+(0.3-0)^2]
d = 0.5 m
d between Q1 and Q3:
d = sqrt[(0-0.4)^2+(-0.3-0)^2]
d = 0.5 m
Through force balance, F between Q2 and Q3 - F between Q1 and Q3:
[tex] F_{net} = \frac{(9x 10^{9})(-3.5)(4) }{ 0.5^{2} } -\frac{(9x 10^{9})(3.5)(4) }{ 0.5^{2} }=-1.008* 10^{12} [/tex]
Thus, the net force is -1 x 10^-12 C
