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CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2010

  • question_answer
    A bat flies at a steady speed of \[4\text{ }m{{s}^{-1}}\] emitting a sound of \[f=90\times {{10}^{3}}Hz\]. It is flying horizontally towards a vertical wall. The frequency of the reflected sound as detected by the bat will be (take velocity of sound in air is \[330\text{ }m{{s}^{-1}}\])

    A) \[88.1\times {{10}^{3}}Hz\]        

    B) \[87.1\times {{10}^{3}}Hz\]

    C) \[92.1\times {{10}^{3}}Hz\]        

    D) \[89.1\times {{10}^{3}}Hz\]

    Correct Answer: C

    Solution :

    Frequency of reflected sound heard by the bat                 \[v'=v\left[ \frac{v-({{v}_{0}})}{v-{{v}_{s}}} \right]\]                 \[=v\left[ \frac{v+{{v}_{0}}}{v-{{v}_{s}}} \right]=v\left[ \frac{v+{{v}_{0}}}{v-{{v}_{b}}} \right]\]                 \[=v\left[ \frac{330+4}{330-4} \right]90\times {{10}^{3}}\]                 \[=92.1\times {{10}^{3}}Hz\]


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