The driver of a car travelling with a speed ' $V_1$ ' $\mathrm{m} / \mathrm{s}$ towards a wall sounds a siren of frequency ' $n$ ' Hz. If the velocity of sound in air is $\mathrm{V} \mathrm{m} / \mathrm{s}$, then the frequency of sound reflected from the wall and as heard by the driver, in Hz , is
- A$\left(\frac{\mathrm{V}+\mathrm{V}_1}{\mathrm{~V}-\mathrm{V}_1}\right) \mathrm{n}$
- B$\left(\frac{V-V_1}{V+V_1}\right) n$
- C$\left(\frac{V_1-V}{V_1+V}\right) n$
- D$\left(\frac{V_1}{V_1-V}\right) n$
✓ Correct answer: A
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