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A train is moving on a straight track with speed `20ms^(-1)`. It is blowing its whistle at the frequency of `1000 Hz`. The percentage change in the frequency heard by a person standing near the track as the train passes him is (speed of sound `= 320 ms^(-1)`) close to :A. `12%`B. `6%`C. `18%`D. `24%` |
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Answer» Correct Answer - A Observer is stationary and source is moving. During approach, `f_(1) = f((nu)/(nu - nu_(s)))` `= 1000((320)/(320 - 20))` `= 1066.67 H_(Z)` During recede, `f_(2) = f((nu)/(nu + nu_(s)))` `= 1000((320)/(320 + 20)) = 941.18 H_(Z)` `|%` change in frequency| `= ((f_(1) - f_(2))/(f_(1))) xx 100` `~~ 12%` |
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