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A sounding vehicle passes a stationary observer and the pitch drops by a given ratio: find the speed of the vehicle

The same question, asked 2 times: 3 May 2023 S1*, 11 May 2024 S1. Every wording below, oldest first.

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  1. Question 1

    3 May 2023 S1

    33
    The pitch of a whistle of an engine appears to drop by 30% of original value when it passes a stationary observer. If the speed of sound in air is 350 ms−1350\ \text{ms}^{-1}, then the speed of engine in ms−1\text{ms}^{-1} is

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  2. Question 2

    11 May 2024 S1

    26
    A car sounding a horn of frequency 1000 Hz passes a stationary observer. The ratio of frequencies of the horn noted by the observer before and after passing the car is 11:911:9. If the speed of sound is vv, the speed of the car is

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