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JEE Main & Advanced Physics Wave Mechanics Question Bank Doppler's Effect

  • question_answer
    The driver of a car travelling with speed 30 metres per second towards a hill sounds a horn of frequency 600 Hz. If the velocity of sound in air is 330 metres per second, the frequency of the reflected sound as heard by the driver is                    [MP PMT 1996]

    A)            720 Hz                                     

    B)            555.5 Hz

    C)            550 Hz                                     

    D)            500 Hz

    Correct Answer: A

    Solution :

               From the figure, it is clear that Frequency of reflected sound heard by the driver. \[n'=n\,\left[ \frac{v-(-{{v}_{o}})}{v-{{v}_{s}}} \right]=n\,\left[ \frac{v+{{v}_{o}}}{v-{{v}_{s}}} \right]=n\,\left[ \frac{v+{{v}_{car}}}{v-{{v}_{car}}} \right]\]    \[=600\,\left[ \frac{330+30}{330-30} \right]=720\,Hz.\]


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