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.Two automobiles are equipped with the same single-frequency horn. When one is at rest and the other is moving toward an observer at 14 m/s, a beat frequency of 5.1 Hz is heard. What is the frequency the horns emit? Assume T = 20°C.

  • physics -

    The frequency difference is 5.1 Hz

    (1 + V/a)*f - f = (V/a)*f = 5.1
    a is the sound speed (340 m/s), and
    V = 14 m/s

    Solve for f.

    f = 124 Hz

    I did not use the exact formula for a doppler-shifted moving source, but this should be close enough.

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