question_answer

A speeding motorcyclist sees traffic jam ahead of him. He slows down to 36 km/h. He finds that traffic has eased and a car moving head of him at 18 km/h is honking at a frequency of 1392 Hz. If the speed of sound is 343 m/s, the frequency of the honk as heard by him will be                                                                                                         [NEET 2014]

A)  1332 Hz

B)          1372 Hz           

C)  1412 Hz  

D) 1454 Hz

Correct Answer: C

Solution :

\[\Rightarrow \]   As both observer and source are moving, we can use the formula of apparent frequency as

\[f={{f}_{0}}\left( \frac{v+{{v}_{0}}}{v+{{v}_{s}}} \right)\]

\[=1392\left[ \frac{343+10}{343+5} \right]\]

\[=1392\left[ \frac{353}{348} \right]Hz\]

\[=1412\]