1. Tardigrade
  2. Question
  3. Physics
  4. A police car with a siren of frequency 8 kHz is moving with uniform velocity 36 km/hr towards a tall building which reflects the sound waves. The speed of sound in air is 320 m/s. The frequency of the siren heard by the car driver is

Question Error Report

Thank you for reporting, we will resolve it shortly

Back to Question

Q. A police car with a siren of frequency $8\, kHz$ is moving with uniform velocity $36\, km/hr$ towards a tall building which reflects the sound waves. The speed of sound in air is $320 \,m/s$. The frequency of the siren heard by the car driver is

IIT JEEIIT JEE 2011Waves

Solution:

$36\, km/h = 36 \times \frac{5}{18} = 10\, m/s$
Apparent frequency of sound heard by car driver (observer) reflected from the building will be
$f'=f\bigg(\frac{v+v_0}{v-v_s}\bigg)=8\bigg(\frac{320+10}{320-10}\bigg)=8.5\, kHz$
$\therefore $ Correct option is (a).

Solution Image