Answer :
The potential energy of the system when a third point charge q = -4.20 nC is placed at point C is -5.53 x 10^-6 J.
The potential energy of a system of point charges is given by the equation U = k(q1q2)/r, where U is the potential energy, k is the Coulomb constant (9 x 10^9 Nm^2/C^2), q1 and q2 are the charges, and r is the separation distance between the charges. In this case, we have two charges (+9.7 nC and -9.7 nC) located 8.00 cm apart.
The potential energy between these two charges is zero since the charges are equal in magnitude and opposite in sign. When a third charge q = -4.20 nC is placed at point C, the potential energy is calculated by substituting the values into the equation. The result is -5.53 x 10^-6 J. The negative sign indicates that the system is in a stable configuration.
To learn more about potential energy click here: brainly.com/question/24284560
#SPJ11