A whistle giving out $450 Hz$ approaches a stationary observer at a speed of $33 m/s.$ The frequency heard by the observer in $Hz$ is
A$409$
B$429$
C$517$
D$500$
IIT 1997, Medium
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D$500$
d (d)The apparent frequency heard by the observer is given by
$n' = \frac{v}{{v - {v_S}}}n$= $\frac{{330}}{{330 - 33}} \times 450 = \frac{{330}}{{297}} \times 450 = 500$$Hz$
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