## Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

The force on the 1.0 nC charge is $3.1\times 10^{-4}~N$ directed upwards.
By symmetry, the horizontal component of each force on the 1.0 nC charge cancels out. The net force on the 1.0 nC charge is the sum of the vertical component of each force. Since positive charges repel each other, the net force is directed upward. $F = 2\times \frac{(k)(1.0~nC)(2.0~nC)}{r^2}~sin(60^{\circ})$ $F = 2\times \frac{(9.0\times 10^9~N~m^2/C^2)(1.0\times 10^{-9}~C)(2.0\times 10^{-9}~C)}{(0.010~m)^2}~sin(60^{\circ})$ $F = 3.1\times 10^{-4}~N$ The force on the 1.0 nC charge is $3.1\times 10^{-4}~N$ directed upwards.