Which of the following graphs represents a plot of the frequency f′ of a sound wave perceived by a stationary observer versus the speed vs of the source approaching towards him?
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Which of the following graphs represents a plot of the frequency f′ of a sound wave perceived by a stationary observer versus the speed vs of the source approaching towards him?

G1 Physics · Accepted Answer

Step 1: For sound, f' = f(v ± vₒ)/(v ∓ vₛ), with velocities taken relative to the medium. Step 2: Choose signs for approach/recession; for an echo/reflection apply the Doppler shift twice. Step 3: If two frequencies are heard, take their difference for beats. Final: A: Image 1.