Question

Two sources of sound $S_1$ and $S_2$ produce sound waves of same frequency $660Hz$. A listener is moving from source $S_1$ towards $S_2$ with a constant speed $um/s$ and he hears $10beats/s$. The velocity of sound is $330m/s$. Then, $u$ equals:

• A. $2.5m/s$
• B. $15.0m/s$
• C. $5.5m/s$
• D. $10.0m/s$

Answer 1

The correct option is A $2.5m/s$

$f=660Hz,v=330=m/s$
$f_1=\left(\frac{v-u}{v}\right)$
$f_2=f\left(\frac{v+u}{v}\right)$
$f_2-f_1=\frac{f}{v}[v+u-(v-u\left)\right]$
$10=f_2-f_1=\frac{f}{v}\left[2u\right]$
$u=2.5m/s$