Final answer:
The electric potential at point A due to two identical 4.0-µC charges placed on the y-axis at y = +/-4.0 m is twice the magnitude of the potential due to a single charge.
Step-by-step explanation:
To determine the electric potential at point A, we need to consider the contribution from each of the charges. The electric potential at a point due to a point charge is given by the formula V=kQ/r, where V is the potential, k is the Coulomb's constant (9x10^9 Nm^2/C^2), Q is the charge, and r is the distance from the charge to the point.
Since we have two identical 4.0-µC charges, the electric potential at point A due to each charge will be the same magnitude. The distance from each charge to point A is 5.0 m (3.0 m along the x-axis and 4.0 m along the y-axis), so the electric potential due to each charge is V=kQ/r=k(4.0x10^-6 C)/(5.0 m). Thus, the total electric potential at point A is twice the magnitude of the potential due to a single charge, so Vtotal=2(kQ/r)=2(9x10^9 Nm^2/C^2)(4.0x10^-6 C)/(5.0 m).