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JEE Main & Advanced Physics Wave Mechanics Question Bank Self Evaluation Test - Waves

  • question_answer
    Two trains are moving towards each other with speeds of 20m/s and 15 m/s relative to the ground. The first train sounds a whistle of frequency 600 Hz. The frequency of the whistle heard by a passenger in the second train before the train meets, is (the speed of sound in air is 340 m/s)

    A)  600 Hz

    B)  585 Hz

    C) 645 Hz

    D) 666 Hz

    Correct Answer: D

    Solution :

    [d]  \[v'=v\left( \frac{v+{{v}_{D}}}{v-{{v}_{S}}} \right)\] Here, \[v=600Hz,\,\,{{v}_{D}}=15m/s\] \[{{v}_{s}}=20,m/s,\,\,\,\,v=340m/s\] \[\therefore \,\,\,\,v'=600\left( \frac{355}{320} \right)\approx 666\,Hz\]


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