A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of 15 ms -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 ms -1 )

Question

A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of 15 ms -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 ms -1 ) (A) 765 Hz (B) 800 Hz (C) 838 Hz (D) 885 Hz

Tardigrade Admin · Accepted Answer

n'=( nv / v - v s ) =800 × (330/315) =838 Hz <img class="img-fluid question-image" alt="image" src="https://cdn.tardigrade.in/img/question/physics/4d53e2c63414c019c75ae8c3753b1b46-.png" /> ∴ Observer hears n'=838 Hz

Q. 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 = $330 m s^{- 1}$ )

765 Hz

800 Hz

838 Hz

885 Hz

$n^{'} = \frac{n v}{v - v _{s}}$
$= 800 \times \frac{330}{315}$
$= 838 Hz$

$∴$ Observer hears
$n^{'} = 838 Hz$

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