Question

A vehicle, with a horn of frequency n is moving with a velocity of 30 m/s in a direction perpendicular to the straight line joining the observer and the vehicle. The observer perceives the sound to have a frequency $n+n_1$. Then (if the sound velocity in air is 300 m/s)

• A. $n_1=0.1n$
• B. $n_1=0$
• C. $n_1=10n$
• D. $n_1=-0.1n$

Answer 1

Answer: (B)

$n_1=0$

Answer 2

The correct option is(B): _n 1_​=0.

$n'=n+n_1=\frac{nv}{v-v_s \,cos\, \theta}=\frac{nv}{v}[\because cos\, 90^\circ=0]$
$n'=n \therefore n_1=0$