試題詳解

14. A particle with mass m and positive charge q starts from rest at the origin under a uniform electric field in the +y-direction and a uniform magnetic field directed out of the page, so . Neglecting gravity, the particle is accelerated by the E field, but the magnetic force bends it to the right and the resulting trajectory is shown in the figure. At point P, the particle reaches its maximum height y_max. What is the velocity of the particle at point P?
(A)
(B)
(C)
(D)

(E)