A car is moving along X -axis with a velocity v=20 m / s. It sounds a whistle of frequency 660 Hz. If the speed of sound is 340 m / s, the apparent frequency heard by the observer O (shown in figure) is:

Question

A car is moving along X -axis with a velocity v=20 m / s. It sounds a whistle of frequency 660 Hz. If the speed of sound is 340 m / s, the apparent frequency heard by the observer O (shown in figure) is: (A) 680 Hz (B) 640 Hz (C) 700 Hz (D) 720 Hz

Tardigrade Admin · Accepted Answer

n'=(v/v-vs cos 60°) n Here v=340 m / s, vs=20 m / s , n=660 Hz n'=(340/340-20 × (1)2) × 660 =(340/330) × 660=680 Hz

Q. A car is moving along $X$ -axis with a velocity $v = 20 m / s$ . It sounds a whistle of frequency $660 Hz$ . If the speed of sound is $340 m / s$ , the apparent frequency heard by the observer $O$ (shown in figure) is:

680 Hz

640 Hz

700 Hz

720 Hz

$n^{'} = \frac{v}{v - v _{s} c o s 6 0 ^{\circ}} n$
Here $v = 340 m / s, v_{s} = 20 m / s, n = 660 Hz$
$n^{'} = \frac{340}{340 - 20 \times \frac{1}{2}} \times 660$
$= \frac{340}{330} \times 660 = 680 Hz$

Q. A car is moving along X -axis with a velocity v=20m/s. It sounds a whistle of frequency 660Hz. If the speed of sound is 340m/s, the apparent frequency heard by the observer O (shown in figure) is: