Three point charges, +6.8 mC, +2.0 mC and -2.1 mC lie along the x-axis at 0 cm, 3.0 cm and 5.2 cm respectively

(To the right is positive) and the Coulomb constant is 8.99 x 10^9
1. What is the force exerted on q1 by the other two charges?
2. What is the force exerted on q2 by the other two charges?
3. What is the force exerted on q3 by the other two charges?

I don't even know where to begin!! Pleeeease help

Let's first calculate the forces between the point charges, using the following formula:

F = k*q1q2 / d^2

where k = Coulomb constant = 8.99 x 10^9 Nm^2 / C^2


F(q1-q2) = (8.99 x 10^9)(6.8 x 10^ -6 C)(2.0 x 10^ -6 C) / (0.03 m)^2 = 135.8 N

F(q2-q3) = (8.99 x 10^9)(2.0 x 10^ -6 C)(-2.1 x 10^ -6 C) / (0.022 m)^2 = - 78.0 N

F(q1-q3) = (8.99 x 10^9)(6.8 x 10^ -6 C)(-2.1 x 10^ -6 C) / (0.052 m)^2 = - 47.5 N



Now, we can calculate the force exerted on each of the point charges (forces going from right to left are added, forces going from right to left are subtracted):


(1) F(q1) = - F(q1-q2) - F(q1-q3) = - (135.8 N) - (-47.5 N) = - 88.3 N

(2) F(q2) = F(q1-q2) - F(q2-q3) = (135.8 N) - (-78.0 N) = 213.8 N

(3) F(q3) = F(q1-q3) + F(q2-q3) = - 47.5 N + (-78.0 N) = - 125.5 N


To check, F(q1) + F(q2) + F(q3) = (- 88.3 N) + (213.8 N) + (- 125.5 N) = 0


Hope this helps...good luck!