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 the sound reflected from the wall and as heard by the driver in Hz is (a) ((V₁)/(V-V₁))n (b) ((V₁-V)/(V+V₁))n (c) ((V+V₁)/(V-V₁))n (d) ((V-V₁)/(V+V₁))n

Answer: (c). 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 (c).

The driver of a car travelling with a speed ' V₁ ' m/s towards a wall… | MHT CET 2024 (2 May, Shift 2)

Q27MHT CET 2024 · 2 MAY · SHIFT 2Medium

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 the sound reflected from the wall and as heard by the driver in Hz is

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Answer: (c)

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 (c).

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Doppler Effect question from MHT CET 2024 (2 May, Shift 2)

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