Waves Ques 76
76. A whistle of frequency $385$ $ Hz$ rotates in a horizontal circle of radius $50 $ $cm$ at an angular speed of $20$ radians $s^{-1}$. The lowest frequency heard by a listener a long distance away at rest with respect to the centre of the circle, given velocity of sound equal to $340$ $ ms^{-1}$, is
[2002]
(a) $396 $ $Hz$
(b) $363 $ $Hz$
(c) $374 $ $Hz$
(d) $385 $ $Hz$
Show Answer
Answer:
Correct Answer: 76.(c)
Solution:
- (c) Velocity of source, $v_s=r \omega$
$ =0.50 \times 20=10$ $ ms^{-1} $
$n^{\prime}=(\frac{v}{v+v_s}) n=\frac{340 \times 385}{340+10}=374 $ $Hz$
BETA
