A siren emitting 600 Hz moves at 170 m/s directly towards a stationary listener. Taking the speed of sound as 340 m/s, what frequency does the listener hear?

Answer and explanation

Correct answer: B. 1200 Hz

  1. Step 1: For a source approaching a stationary observer, .
  2. Step 2: Hz.
Answer
1200 Hz.
Why not the others: 400 Hz: it uses the formula for a receding source. 770 Hz: the speed of the source is added to the frequency. 300 Hz: the ratio is inverted.

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