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JEE Main & Advanced Physics Wave Mechanics Question Bank Self Evaluation Test - Waves

  • question_answer
    A sound source emits frequency of 180 Hz when moving towards a rigid wall with speed 5 m/s and an observer is moving away from wall with speed 5 m/s. Both source and observer moves on a straight line which is perpendicular to the wall. The number of beats per second heard by the observer will be [Speed of sound = 355 m/s]

    A)  5 beats/s          

    B)  10 beats/s

    C) 6 beats/s           

    D) 8 beats/s

    Correct Answer: A

    Solution :

    [a] Frequency heard by observer directly coming from source\[=\frac{355-5}{355+5}\times 180=175\]   \[Hz.\,{{f}_{2}}\to \] frequency heard by observer after reflection \[=\left[ \frac{355}{355-5}\times  \right]\left[ \frac{355-5}{355} \right]\times 180=180\,\,Hz\]  \[{{f}_{2}}-{{f}_{1}}=5\,Hz\]


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