A motor car blowing a horn of frequency 124 vib/sec moves with  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)

  • Option 1)

    109 vib/sec

  • Option 2)

    132 vib/sec

  • Option 3)

    140 vib/sec

  • Option 4)

    248 vib/sec

 

Answers (1)
V Vakul

In the condition source and listener are at the same position i.e car

n' = \frac{c+ v_{car}}{c- v_{car}}v_{0}= \frac{330=20}{330-20}= 140 vib/s

 

Doppler Effect in reflected sound -

\nu _{ap}= \nu _{0}\left ( \frac{C+V_{c}}{C-V_{c}} \right )


 

 

- wherein

C= Speed of sound

V_{c}= Speed of car

 

 


Option 1)

109 vib/sec

This is incorrect

Option 2)

132 vib/sec

This is incorrect

Option 3)

140 vib/sec

This is correct

Option 4)

248 vib/sec

This is incorrect

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