The driver of a car travelling with a speed ' V₁ ' m/s towards a wall sounds a siren of frequency ' n ' Hz. If the velocity of sound in air is V m/s, then the frequency of sound reflected from the wall and as heard by the driver, in Hz, is (a) ((V+V₁)/(V-V₁))n (b) ((V-V₁)/(V+V₁))n (c) ((V₁-V)/(V₁+V))n (d) ((V₁)/(V₁-V))n

Answer: (a). Wall receives n₁ = n (V)/(V - V₁) (source approaching). Wall re-emits n₁; driver approaches it: n' = n₁ (V + V₁)/(V) = ((V + V₁)/(V - V₁))n So the answer is (a).

The driver of a car travelling with a speed ' V₁ ' m/s towards a wall… | MHT CET 2024 (15 May, Shift 1)

Q26MHT CET 2024 · 15 MAY · SHIFT 1Medium

Doppler Effect

The driver of a car travelling with a speed ' $V_1$ ' $\text{m/s}$ towards a wall sounds a siren of frequency ' $n$ ' Hz. If the velocity of sound in air is $V\text{ m/s}$ , then the frequency of sound reflected from the wall and as heard by the driver, in Hz, is

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Answer: (a)

Wall receives $n_1 = n\,\dfrac{V}{V - V_1}$ (source approaching).
Wall re-emits $n_1$ ; driver approaches it: $n' = n_1\,\dfrac{V + V_1}{V} = \left(\dfrac{V + V_1}{V - V_1}\right)n$
So the answer is (a).

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Doppler Effect question from MHT CET 2024 (15 May, Shift 1)

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