A car’s horn produces a constant frequency of 350 Hz as it passes by Suzy. What is the best estimate of the frequency Suzy hears after the car passes her?

After the car passes Suzy, it is moving away from her, so the sound waves reaching her are spread farther apart. This lowers the frequency she hears below the horn’s emitted frequency of 350 Hz. Of the choices, 330 Hz is the best estimate; 350 Hz would mean no Doppler shift.

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