A motor car blowing a horn of frequency 124vib/sec moves with a velocity 72 km/hr towards a tall wall. The frequency of the reflected sound heard by the driver will be (velocity of sound in air is 330 m/s) 

(1) 109 vib/sec

(2) 132 vib/sec

(3) 140 vib/sec

(4) 248 vib/sec

(3) Similar to previous question

The frequency of reflected sound heard by the driver

n'=nv(v0)vvs=nv+v0vvs

=124330+(72×5/18)330(72×5/18)= 140 vibration/sec.

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