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JEE Main & Advanced JEE Main Paper (Held On 09-Jan-2019 Evening)

  • question_answer
    A musician using an open flute of length 50 cm produces second harmonic sound waves. A person runs towards the musician from another end of a hall at n speed of 10 km/h. If the wave speed is 330 m/s, the frequency heard by the running person shall be close to: [JEE Main Online Paper (Held On 09-Jan-2019 Evening]

    A) 753 Hz                                     

    B) 666 Hz

    C) 500 Hz             

    D)               333 Hz

    Correct Answer: B

    Solution :

    Frequency of sound source \[=\,\,\frac{2\,V}{2\,L}\] \[=\,\,\frac{330}{50\,\times \,{{10}^{-2}}}\,=\,660\,Hz\] Speed of observer \[=\,\,\frac{10\,\,\times \,\,5}{18}\,m/s\] Apparent frequency \[=\,\,660\,\left( \frac{330+\frac{50}{18}}{330} \right)\]\[=\,\,2\left[ 330+\frac{50}{18} \right)\,\,\,=\,\,666\,Hz\]


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