# physics

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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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