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A siren emitting a sound of frequency 10...

A siren emitting a sound of frequency `1000 H_(Z)` moves away from you towards a cliff at a speed of `10 m//s` .
(a) What is the frequency of the sound you hear coming directly from the sirven ?
(b) What is the frequency of sounds you hear reflected off the cliffb ?
(c) What beat frequency would you hear ? Take the speed of sound in air as `330 m//s` .

Text Solution

Verified by Experts

The situation is as shown in figure.

(a) Frequency of sound reaching directly to us (by S)
`f_(1)=f((V)/(V-V_(S)))f=((330)/(330+10))(1000)`
(b) Frequency of sound which is reflected of from the cliff is same as that received by cliff (treating cliff as a stationary observer)
`f_(2)=f((V)/(V-V_(s)))f=((330)/(330-10))(1000)`
`=1031.3Hz`.
(c) Beat frequency `=f_(2)-f_(1)=60.7Hz`
So, Beat frequency heard is zero.
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