A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of15 m s-1 . Then, the frequency of sound that the observer hears in the echo reflected from the cliff is? (The Velocity of Sound in air=330 m s-1

Here, frequency of sound emitted by siren, v0=800 Hz Speed of source, vs=15 m s-1 Speed of sound in air, v=330 m s-1Apparent frequency of sound at the cliff = frequency heard by observer=v Using Doppler's effect of sound v=vv-vsv0=330330-15×800=330315×800=838.09 Hz≈838 Hz