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CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2001

  • question_answer
    A source having frequency of 240 Hz is moving towards on observer with a speed of 20 m/s. when the observer is moving towards the source with a velocity of 20 m/s. Then apparent frequency heard by the observer, if velocity of sound is 330 m/s, will be:

    A)  268 Hz                                 

    B)  271 Hz

    C)  368 Hz                                 

    D)  250 Hz

    Correct Answer: B

    Solution :

     Speed of source \[{{\upsilon }_{s}}=20\,m/s\] Frequency\[v=240\,Hz\] Speed of observer \[{{\upsilon }_{0}}=20\,\,m/s\] Speed of sound in in air\[~=330\text{ }m/s\] (given) From the Doppler's effect the apparent frequency heard by the observer, when he is moving towards the source is given by: \[v'=\left( \frac{\upsilon +{{\upsilon }_{0}}}{\upsilon -{{\upsilon }_{s}}} \right)\times v\] \[=\left( \frac{330+20}{330-20} \right)\times 246=27.96\] \[=271\,Hz\]


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