Wave Motion 4 Question 20
19. A bus is moving towards a huge wall with a velocity of $5 ms^{-1}$. The driver sounds a horn of frequency $200 Hz$. The frequency of the beats heard by a passenger of the bus will be ….. Hz. (Speed of sound in air $=342 ms^{-1}$ )
(1992, 2M)
True / False
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Answer:
Correct Answer: 19. (a)
Solution:
- Frequency of refracted sound
$$ \begin{gathered} \overrightarrow{v _O}=5 m / s \\ f^{\prime}=f\left(\frac{\stackrel{\rightharpoonup}{v+v _o}}{v-v _s}\right)=200\left(\frac{342+5}{342-5}\right) Hz=205.93 Hz \end{gathered} $$
$\therefore$ Beat frequency $=f^{\prime}-f=(205.93-200)$
$$ =5.93 Hz \simeq 6 Hz $$
