Q137 / 150 · MHT CET 2024 (11 May Shift 1) · Physics

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.
Correct answer
D
Twice the velocity of sound towards the source.

Solution

Applying Doppler's effect to sound waves, we can write, $n^{\prime}=n\left(\frac{v+v_0}{v}\right)=n\left(1+\frac{v_0}{v}\right)$. $\begin{array}{ll} & \mathrm{n}^{\prime}=3 n \quad \ldots . \text { (given) } \\ \therefore \quad & 3 n=n\left(1+\frac{v_0}{v}\right) \\ \therefore \quad & 3=1+\frac{v_0}{v} \\ \therefore \quad & \frac{v_0}{v}=2 \quad \Rightarrow v_0=2 v \end{array}$

Hence, the correct answer is option: 'D'.

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