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JEE Main & Advanced Sample Paper JEE Main Sample Paper-33

  • question_answer
    A wall is moving with velocity u and a source of sound moves with velocity \[\frac{u}{2}\] in the same direction as shown in the figure. Assuming that the sound travels with velocity 10 u. The ratio of incident sound wavelength on the wall to the reflected sound wavelength by the wall, is equal to:

    A)  \[9:11\]

    B)                     \[11:9\]

    C)  \[4:5\]         

    D)                     \[5:4\]

    Correct Answer: A

    Solution :

    \[v=f\lambda \]             \[{{f}_{reflected.}}=\left( \frac{10u}{10u+u} \right){{f}_{received}}\] \[\frac{{{\lambda }_{rec}}}{{{\lambda }_{ref}}}\,=\left( \frac{10u-u}{{{f}_{rec}}} \right)\,\times \frac{{{f}_{ref}}}{10u}\,=\frac{9u}{{{f}_{rec}}}\,\frac{\left( \frac{10u}{11u}\,\times {{f}_{rec}} \right)}{10u}=\frac{9}{11}\]


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