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JEE Main & Advanced JEE Main Paper (Held On 11 April 2014)

  • question_answer
    Two factories are sounding their sirens at 800 Hz. A man goes from one factory to other at a speed of 2m/s. The velocity of sound is 320 m/s. The number of beats heard by the person in one second will be:   [JEE Main Online Paper ( Held On 11 Apirl  2014 )

    A) 2                                             

    B) 4

    C) 8                                             

    D) 10

    Correct Answer: D

    Solution :

    Given: Frequency of sound produced by siren, f = 800 Hz Speed of observer, \[u=2m/s\] Velocity of sound, \[v=320\text{ }m/s\] No. of beats heard per second = ? No. of extra waves received by the observer per second \[=\pm 4\lambda \] \[\therefore \]No. of beats/ sec\[=\frac{2\times 2}{\frac{320}{800}}\left( \because \lambda =\frac{V}{f} \right)\] \[=\frac{2\times 2\times 800}{320}=10\]


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