What is the magnitude of the force f on the 1.0 nc charge in the figure ?

In this problem, the 2.0 nC charges both act forces of equal magnitude on the 1.0 nC charge. Since there x-components are equal but opposite, they cancel out and only the y-components remain and add up. This can be used then to calculate for the magnitude of the total electrostatic force.

F = 2 * q1 * q2 / 4 / pi / eps_0 / r^2 * sqrt(3) / 2
F = 2 * 1.0e-9 * 2.0e-9 / 4 / pi / 8.854e-12 / (1.0e-2)^2 * sqrt(3) / 2
F = 3.11e-4 N

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