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MHT CET 2026 (13 May, Shift 2) · Doppler Effect

Doppler Effect question from MHT CET 2026 (13 May, Shift 2)

Q8MHT CET 2026 · 13 MAY · SHIFT 2Medium

Doppler Effect

Two sirens situated one km apart are producing sound of frequency $330$ Hz. The observer starts moving from one siren to the other with a speed of $2$ m/s. If the speed of sound is $330$ m/s, What will be the beat frequency heard by the observer?

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Answer: (b)

Observer moves away from one siren and towards the other with $u = 2$ m/s.
Towards: $f_1 = f\frac{v+u}{v} = 330 \times \frac{332}{330} = 332$ Hz
Away: $f_2 = f\frac{v-u}{v} = 330 \times \frac{328}{330} = 328$ Hz
Beat frequency $= f_1 - f_2 = 4$ Hz
So the answer is (b) $4$ Hz.

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