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Apparent frequency (Doppler effect) when a source or observer moves along a line

This type of question, asked 5 times: 2021 Paper 20, 27 Jun 2022, 25 Jan 2023, 29 Jan 2023, 11 Apr 2023. All 5 questions below, oldest first.

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  1. Question 1

    2021 Paper 20

    26
    Two cars XX and YY are approaching each other with velocities 36 km/h36\text{ }km/h and 72 km/h72\text{ }km/h respectively. The frequency of a whistle sound as emitted by a passenger in car XX, heard by the passenger in car YY is 1320 Hz1320\text{ }Hz. If the velocity of sound in air is 340 m/s340\text{ }m/s, the actual frequency of the whistle sound produced is ____\_\_\_\_ Hz.

  2. Question 2

    27 Jun 2022

    16
    An observer moves towards a stationary source of sound with a velocity equal to one-fifth of the velocity of sound. The percentage change in the frequency will be:

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  3. Question 3

    25 Jan 2023

    114
    A train blowing a whistle of frequency 320 Hz320\text{ }Hz approaches an observer standing on the platform at a speed of 66 m/s66\text{ }m/s. The frequency observed by the observer will be ____\_\_\_\_ Hz (given speed of sound =330 ms−1= 330{\text{ }ms}^{- 1})

  4. Question 4

    29 Jan 2023

    5
    A person observes two moving trains, 'A' reaching the station and 'B' leaving the station with equal speed of 30 m/s30\text{ }m/s. If both trains emit sounds with frequency 300 Hz300\text{ }Hz, (Speed of sound: 330 m s\frac{330\text{ }m}{\text{ }s} ) approximate difference of frequencies heard by the person will be:

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  5. Question 5

    11 Apr 2023

    92
    A car PP travelling at 20 ms−120{\text{ }ms}^{- 1} sounds its horn at a frequency of 400 Hz400\text{ }Hz. Another car Q is travelling behind the first car in the same direction with a velocity 40 ms−140{\text{ }ms}^{- 1}. The frequency heard by the passenger of the car QQ is approximately [Take, velocity of sound =360 ms−1= 360{\text{ }ms}^{- 1} ]

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