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 fd is given by

fd = fs(v + vd)(v - vs)       (1)    , Here v is the velocity of sound ( taken as 343 m/s), vd is the velocity of the detector and it is positive since detector is moving towards the source, vs is the velocity of source and is zero (source is stationary) and fs is the frequency of source.

Substituting corresponding values in (1), we get

fd300343+5343      (where the velocity is converted into m/s from km/hr)

Then fd = 304.37 Hz  and  fd -fs = 4.37 Hz

Thus solved


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