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A motor car blowing a horn of frequency ...

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

A

109 vib/sec

B

132 vib/sec

C

140 vib/sec

D

248 vib/sec

Text Solution

Verified by Experts

The correct Answer is:
C
According to image concept.
`f.=f((v+v_c)/(v-v_c))`
`=124 ((330+20)/(330-20))" " ["as " v_c= 72 xx5/18 =20 m//s]`
= 140 vib/ sec
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