試題詳解

21. As shown in Figure 7, a ring of radius R=0.03 (m) lies in a plane with its center at the origin. The ring has a uniformly distributed positive charge Q = 9.0×(Coul). A small charged particle with mass m = 3.8×(kg) and positive charge q = 7.0×(Coul) is placed at a distance d = 0.05 (m) from the axis of the ring and released. Find the speed v of the Q particle when it is at an infinite distance from the ring. Assume the effects of gravity are negligible.

(A) 2.26 (m/sec)
(B) 2.33 (m/sec)
(C) 2.57 (m/sec)
(D) 3.21 (m/sec)