As shown in Fig. 21-17, a point charge of \( +Q \) is placed at the centroid of an equilateral triangle. When a second charge of \( +Q \) is placed at one of the triangle's vertices, an electrostatic force of \( 4.0 \mathrm{~N} \) acts on it. What is the magnitude of the force that acts on the center charge due to a third charge of \( +Q \) placed at one of the other vertices?
FIGURE 21-17
zero
\( 16 \mathrm{~N} \)
4.0 N
\( 2.0 \mathrm{~N} \)
\( 8.0 \mathrm{~N} \)