# A car is moving with a speed of 18km/hr . The car pases a check post ,where a siren is producing sound waves of frequency 300 Hz . Determine the change in the frequency heard by the driver of the car just as he pases the check post

Dear Student,

The equation for the detected frequency f

_{d}is given by

${f}_{d}={f}_{s}\frac{(v+{v}_{d})}{(v-{v}_{s})}\left(1\right)$ , Here v is the velocity of sound ( taken as 343 m/s), v

_{d}is the velocity of the detector and it is positive since detector is moving towards the source, v

_{s}is the velocity of source and is zero (source is stationary) and f

_{s}is the frequency of source.

Substituting corresponding values in (1), we get

f

_{d}= $300\left(\frac{343+5}{343}\right)$ (where the velocity is converted into m/s from km/hr)

**Then f**

_{d}= 304.37 Hz and f_{d}-f_{s}= 4.37 HzThus solved

Regards

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