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A traffic policeman standing on a road sounds a whistle emitting the main frequency of 2.00 kHz. What could be the apparent frequency heard by a scooter driver approaching the policeman at a speed of `36.0km h^(-1) ?` Speed of sound in air `=340 m s^(-1).`

Text Solution

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The correct Answer is:
B
Let, u = Velocity of sound
`upsilon_m = velocity of the medium
`upsilon_0 = velocity of the observer
`upsilon_s = velocity of the sources
`f = ((vec u + vec upsilon_m - vec upsilon_0)/(upsilon + upsilon_m - upsilon_s))F`
Using sign conventions in Doppler's effect
`upsilon_m = 0, u = 340 m//s,`
`upsilo _s = 0 and vec upsilon_0 = -10 m`
(36 km//h = 10m//s)`
`f = ((340 + 0-9 - 10)/(340 + 0-0))xx2 kHz`
` =(350xx2)/(340)kHz`
=2.06 kHz.
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