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An observer standing on a railway crossi...

An observer standing on a railway crossing receives frequencies 2.2 kHz and 1.8 kHz when the tran approaches and recedes from the observer. Find the velocity of the train (speed of sound in air is 300 m/s).

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The correct Answer is:
`30 ms^(-1)`
From the relation `f'=f((V)/(Vpm V_(s)))`
we have `2.2=f[(300)/(300-V_(T))]`….(i)
and `1.8=f[(330)/(300+V_(T))]`…(ii)
Here, `V_(Y) = V_(S)` = velocity of source/train
Solving equation (i) and (ii),we get `V_(T) = 30 m//s`.
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