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MHT CET 2024 (3 May, Shift 1) · Doppler Effect

Doppler Effect question from MHT CET 2024 (3 May, Shift 1)

Q25MHT CET 2024 · 3 MAY · SHIFT 1Medium

Doppler Effect

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 $350\text{ ms}^{-1}$ , then the speed of engine in $\text{ms}^{-1}$ is

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Answer: (d)

After passing, the engine recedes and the heard pitch is 70% of the original: $f' = f\,\dfrac{v}{v + u} = 0.7f$ .
$350 = 0.7(350 + u) \Rightarrow 350 + u = 500$
So the answer is (d) $u = 150\text{ m/s}$ .

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