Wave Motion 4 Question 33
31. A source of sound of frequency $256 Hz$ is moving rapidly towards a wall with a velocity of $5 m / s$. How many beats per second will be heard by the observer on source itself if sound travels at a speed of $330 m / s$ ?
(1981, 4M)
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Answer:
Correct Answer: 31. 7.87 Hz
Solution:
- Frequency heard by the observer due to $S^{\prime}$ (reflected wave)
$$ \begin{aligned} f^{\prime} & =f\left(\frac{v+v _o}{v-v _s}\right)=256\left(\frac{330+5}{330-5}\right) \\ & =263.87 Hz \end{aligned} $$
$\therefore$ Beat frequency $f _b=f^{\prime}-f=7.87 Hz$
