『\"One Question a Day\" Physics
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The train is moving in a straight line at a speed of 25 m/s, and the frequency of its whistle is 500 Hz. Let the speed of sound in air be 340 m/s. A person is standing next to the railway tracks. As the train passes by him, the frequency change of the whistle sound is ( ) (C) 432 Hz (B) 466 Hz (D) 74 Hz (A) 540 Hz. The reference answer can be seen after responding; scoring is possible by identifying the correct key point. Answer: D
Trains arrive frequently, but depart less often.