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MHT CET 2023 (11 May, Shift 1) · Doppler Effect

Doppler Effect question from MHT CET 2023 (11 May, Shift 1)

Q35MHT CET 2023 · 11 MAY · SHIFT 1Medium

Doppler Effect

A car sounding a horn of frequency $1000\text{ Hz}$ passes a stationary observer. The ratio of frequencies of the horn noted by the observer before and after passing the car is $11 : 9$ . If the speed of sound is ' $v$ ', the speed of the car is

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Answer: (d)

Before: $f_1 = f\,\dfrac{v}{v - u}$ ; after: $f_2 = f\,\dfrac{v}{v + u}$ , so $\dfrac{f_1}{f_2} = \dfrac{v + u}{v - u}$ .
$\dfrac{v + u}{v - u} = \dfrac{11}{9} \Rightarrow 9v + 9u = 11v - 11u \Rightarrow 20u = 2v$
So the answer is (d) $u = v/10$ .

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