試題詳解

1. A jet plane in straight horizontal flight passes over your head. When the plane is directly above you, the sound seems to come from a point behind the plane in a direction 45° from the vertical. The speed of the sound is vs. The speed of the plane is about:
(A) vs
(B) 0.5vj
(C) 0.7 Ivj
(D) 1.41vj
(E) 2vs.