An employee of a factory moving away from his workplace by a car listens to the siren of the factory. He drives the car at the speed of 72 kmh$-$1 in the direction of wind which is blowing at 72 kmh$-$1 speed. Frequency of siren is 720 Hz. The employee hears an apparent frequency of ____________ Hz.
(Assume speed of sound to be 340 ms$-$1)
Answer (integer)
680
Solution
Here, the apparent frequency is given by
<br/><br/>
$$
\begin{aligned}
&f^{\prime}=f\left(\frac{V-V_{0}}{V+V_{s}}\right)=720\left(\frac{(340+20)-20}{(340+20)-0}\right) \\\\
&=\frac{720 \times 340}{360}=680 \mathrm{~Hz}
\end{aligned}
$$
About this question
Subject: Physics · Chapter: Waves · Topic: Wave Motion and Types
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