A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of 15   m  s - 1 . Then, the frequency of sound that the observer hears in the echo reflected from the cliff is (Take velocity of sound in air = 330   m  s - 1 )

Step-by-step solution

Given here, f o = 800  H z V s = 15   m   s - 1 Using Doppler's effect, the frequency of sound that the observer hears in the echo reflected from the cliff is f a = f o V + V o V − V s ⇒ f a = 330 330 - 15 × 800 = 330 315 × 800 f a = 838   H z