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

  • question_answer
    A whistle revolves in a circle with an angular speed of 20 rad/sec using a string of length 50 cm. If the frequency of sound from the whistle is 385 Hz, then what is the minimum frequency heard by an observer, which is far away from the centre in the same plane? (v = 340 m/s) [CBSE PMT 2002]

    A)            333 Hz                                     

    B)            374 Hz

    C)            385 Hz                                     

    D)            394 Hz

    Correct Answer: B

    Solution :

               Minimum frequency will be heard, when whistle moves away from the listener. \[{{n}_{\min }}=n\,\left( \frac{v}{v+{{v}_{s}}} \right)\] where \[v=r\omega =0.5\times 10=1\,m/s\] Þ \[{{n}_{\min }}=385\,\left( \frac{340}{340+10} \right)=374Hz.\]


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