question_answer

A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of \[15\,m{{s}^{-1}}\]. Then, the frequency of sound that the observer hears in the echo reflected from the cliff is :      [NEET - 2016] (Take velocity of sound in air \[=330\,m{{s}^{-1}}\])

A)  765 Hz            

B)       800 Hz

C)  838 Hz            

D)       885 Hz

Correct Answer: C

Solution :

\[n'=\frac{v}{v-{{v}_{s}}}{{n}_{0}}\]

\[n'=\frac{330}{330-15}(800)=\frac{330\times 800}{315}=383Hz\]