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)

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Answer:

Correct Answer: 19. 6

Solution:

  1. Frequency of refracted sound

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$$ \begin{gathered} f^{\prime}=f\left(\frac{\stackrel{\rightharpoonup}{v+v _o}}{v-v _s}\right)=200\left(\frac{342+5}{342-5}\right) Hz=205.93 Hz \end{gathered} $$

$\therefore$ Beat frequency $=f^{\prime}-f=(205.93-200)$

$$ =5.93 Hz \simeq 6 Hz $$



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