With what velocity an observer should move relative to a stationary source so that a sound of triple the frequency of source is heard by an observer? (a) Same as velocity of sound towards the source. (b) Same as velocity of sound away from the source. (c) Half the velocity of sound towards the source. (d) Twice the velocity of sound towards the source.

Answer: (d). Observer moving towards a stationary source: f' = f (v + u)/(v). 3f = f (v + u)/(v) ⇒ u = 2v So the answer is (d) twice the speed of sound, towards the source.

With what velocity an observer should move relative to a stationary… | MHT CET 2024 (11 May, Shift 1)

Q22MHT CET 2024 · 11 MAY · SHIFT 1Medium

Doppler Effect

With what velocity an observer should move relative to a stationary source so that a sound of triple the frequency of source is heard by an observer?

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Answer: (d)

Observer moving towards a stationary source: $f' = f\,\dfrac{v + u}{v}$ .
$3f = f\,\dfrac{v + u}{v} \Rightarrow u = 2v$
So the answer is (d) twice the speed of sound, towards the source.

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Doppler Effect question from MHT CET 2024 (11 May, Shift 1)

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