Waves - Result Question 76
78. 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) $385 Hz$
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Answer:
Correct Answer: 78. (c)
Solution:
- (c) Velocity of source, $v_s=r \omega$
$ =0.50 \times 20=10 ms^{-1} $
$n^{\prime}=(\frac{v}{v+v_s}) n=\frac{340 \times 385}{340+10}=374 Hz$
