Question

The siren of a police car at rest emits at a predominant frequency of 1980 Hz. What frequency will you hear if you are at rest and the police car moves at 34.3.0m/s (a) toward you, and (b) away from you? Please Explain

Answer 1

Answer:

(a) 1782 Hz (b) 2178 Hz

Explanation:

The predominant frequency =1980 Hz

The speed of the police car =34.3 m/sec

The speed of sound in air =343 m/sec

(a) When the car moves towards you

According to Doppler's effect

$f=f_0\frac{v-v_s}{v}=1980\times \frac{343-34.3}{343}=1782Hz$

(b) When the car moves away from you

$f=f_0\frac{v+v_s}{v}=1980\times \frac{343+34.3}{343}=2178Hz$