A siren emitting sound of frequency 800 ~Hz is going away from a static listener with a speed of 30 ~m / s . Frequency of the sound to be heard by the listener is (Take velocity of sound as 300 ~m / s )

Step-by-step solution

Frequency of siren (v)=800 ~Hz Speed of siren (v_s )=v-v₀=30 ~m / s Velocity of listener (v₀ )=0 and velocity of sound (v)=330 ~m / s . From the Doppler's law, frequency heard from siren when it is going away from a listener is = ( v-v₀ v+v_s ) v= ( 330-0 330+30 ) 800=733.3 ~Hz