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A train standing at the outer signal of ...

A train standing at the outer signal of a railway station blows a whistle of frequency 400Hz in still air. (i) What is the frequency of the whistle for a platform observer when the train (a) approaches the platform with a speed of `10 ms^(-1)`. (b) recedes from the platform with a speed of `10ms^(-1)` ? (ii) What is the speed of sound in each case? The speed of sound in still air can be taken as `340ms^(-1)`.

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(i) (a) 412Hz, (b) 389Hz, (ii) `340 ms^(-1)` in each case
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