A Charge Q = -820 NC Is Uniformly Distributed on a Ring

Multiple Choice

A charge Q = -820 nC is uniformly distributed on a ring of 2.4 m radius. A point charge q = +530 nC is fixed at the center of the ring. Points A and B are located on the axis of the ring, as shown in the figure. What is the minimum work that an external force must do to transport an electron from B to A? (e = 1.60 × 10^-19 C, k = 1/4πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

A) -8.7 × 10^-17 J
B) +7.2 × 10^-18 J
C) +1.0 × 10^-16 J
D) +8.7 × 10^-17 J
E) -7.2 × 10^-18 J