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JCECE Engineering JCECE Engineering Solved Paper-2010

  • question_answer
    Two trains are moving towards each other with speeds of \[20\,\,m/s\] 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 :

    The perceived frequency \[(f')\] is related to the actual frequency \[({{f}_{0}})\] and the relative speeds of the source \[({{v}_{s}})\] and observer \[({{v}_{0}})\] and the speed \[(v)\] of waves in the medium is given by                 \[f'={{f}_{o}}\left( \frac{v+{{v}_{o}}}{v-{{v}_{s}}} \right)\] Given,\[v=340\,\,m/s,\,\,{{v}_{o}}=15\,\,m/s,\,\,{{v}_{s}}=20\,\,m/s\] \[\therefore \]  \[f'=600\times \left( \frac{340+15}{340-20} \right)\]                     \[=\frac{355}{320}\times 600=666\,\,Hz\]


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