阿摩線上測驗
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9. A stationary listener hears frequency f₁ from a source moving directly toward the listener with a speed of 20.0 m/s. When the listener then moves directly toward the source with a speed of 30.0 m/s, the detected frequency f₂ differs from f₁ by 33.0 Hz. What is the frequency (Hz) of the source? Take the speed of sound to be 340 m/s. (A) 1.14×10³ (B) 899 (C) 352 (D) 2.24×10³ (E) 707