A police car with a siren of frequency 8kHz is moving with a uniform velocity 36kmh- 1 towards a tall building which reflects the sound waves. The speed of sound in air is 320ms- 1 . The frequency of the siren heard by the car driver is

Question

A police car with a siren of frequency 8kHz is moving with a uniform velocity 36kmh- 1 towards a tall building which reflects the sound waves. The speed of sound in air is 320ms- 1 . The frequency of the siren heard by the car driver is (A) 8.5kHz (B) 8.25kHz (C) 7.25kHz (D) 7.5kHz

Tardigrade Admin · Accepted Answer

36 kmh- 1 =36× (5/18) =10ms- 1 <img class="img-fluid question-image" alt="Solution" src="https://cdn.tardigrade.in/q/nta/p-hnsoavhsbdnipec2.jpg" /> Apart frequency of sound heard by car driver (observer) fâ² â²=f((v + vo/v - vs)) =8((320 + 10/320 - 10)) fâ² â²=8.5 kHz

Q. A police car with a siren of frequency $8 k Hz$ is moving with a uniform velocity $36 km h^{- 1}$ towards a tall building which reflects the sound waves. The speed of sound in air is $320 m s^{- 1}$ . The frequency of the siren heard by the car driver is

$8.5 k Hz$

$8.25 k Hz$

$7.25 k Hz$

$7.5 k Hz$

$36 km h^{- 1}$ $= 36 \times \frac{5}{18}$
$= 10 m s^{- 1}$

Apart frequency of sound heard by car driver (observer)
$f^{''} = f (\frac{v + v _{o}}{v - v _{s}})$
$= 8 (\frac{320 + 10}{320 - 10})$
$f^{''} = 8.5 k Hz$

Q. A police car with a siren of frequency 8kHz is moving with a uniform velocity 36kmh−1 towards a tall building which reflects the sound waves. The speed of sound in air is 320ms−1 . The frequency of the siren heard by the car driver is

8.5kHz

8.25kHz

7.25kHz

7.5kHz