試題詳解

43. When an ambulance passes in front of an observer, the sound frequency is 440 Hz when the ambulance is approaching, and the frequency drops to 400 Hz when the ambulance is moving away. What is the speed of the ambulance? (Assume the speed of sound is 345 m/s at that time.)
(A) 13.8 m/s
(B) 14.0 m/s
(C) 14.4 m/s
(D) 15.4 m/s
(E) 16.4 m/s