Question

A siren emits sound of frequency $1000Hz$, it moves away from the observer towards a cliff with a speed of $10m{s}^{-1}$. Then, the frequency of sound heard by observer coming directly from the siren is :

• A. Less than $1000Hz$
• B. Greater than $1000Hz$
• C. Equal to $1000Hz$
• D. No sound is heard

Answer 1

The correct option is A Less than $1000Hz$

Sound heard

$f_1=f_0\left(\frac{v}{v+v_s}\right)$

$v_s=10m{s}^{-1}$

$f_1=\left(\frac{330}{330+10}\right)\times 1000$

$f_1=\frac{33}{34}\times 1000$ is less than $1000Hz$.