Two automobiles are equipped with the same singlefrequency horn. When one is at rest and the other is moving toward the first at 20 m/s , th

Question

Two automobiles are equipped with the same singlefrequency horn. When one is at rest and the other is moving toward the first at 20 m/s , the driver at rest hears a beat frequency of 9.0 Hz.

Requried:
What is the frequency the horns emit?

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Vân Khánh 5 years 2021-08-10T03:35:20+00:00 1 Answers 34 views 0

Answers ( )

  1. thuthuy
    0
    2021-08-10T03:36:27+00:00
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    Answer: f ≈ 8.5Hz

    Explanation: The phenomenon known as Doppler Shift is characterized as a change in frequency when one observer is stationary and the source emitting the frequency is moving or when both observer and source are moving.

    For a source moving and a stationary observer, to determine the frequency:

    f_{0} = f_{s}.\frac{c}{c-v_{s}}

    where:

    f_{0} is frequency of observer;

    f_{s} is frequency of source;

    c is the constant speed of sound c = 340m/s;

    v_{s} is velocity of source;

    Rearraging for frequency of source:

    f_{0} = f_{s}.\frac{c}{c-v_{s}}

    f_{s} = f_{0}.\frac{c-v_{s}}{c}

    Replacing and calculating:

    f_{s} = 9.(\frac{340-20}{340})

    f_{s} = 9.(0.9412)

    f_{s} = 8.5

    Frequency the horns emit is 8.5Hz.

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