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 [AIPMT 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 \[f={{f}_{0}}\left( \frac{v+{{v}_{0}}}{v+{{v}_{s}}} \right)\] \[=1392\left[ \frac{343+10}{343+5} \right]\] \[=1392\left[ \frac{353}{348} \right]Hz\] \[=1412\]