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JEE Main & Advanced JEE Main Solved Paper-2015

  • question_answer
    A train is moving on a straight track with speed \[20m{{s}^{-1}}.\]. 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 \[=320m{{s}^{-1}}\] ) close to [JEE Main Solved Paper-2015 ]

    A) 18%                                                       

    B) 24%                

    C) 6%                                                         

    D) 12%

    Correct Answer: D

    Solution :

                    \[v'=v\left[ \frac{V}{V\pm {{V}_{s}}} \right]\] Frequency increases while approacting and decreases while receding. \[100\frac{\Delta v}{v}=2\left( {}^{{{V}_{s}}}/{}_{V} \right)(100)\] \[=200\left( \frac{20}{320} \right)=12\]


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