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NEET Sample Paper NEET Sample Test Paper-20

  • question_answer
    An ambulance blowing a siren of frequency 700 Hz is travelling slowly towards a vertical reflecting wall with a speed of \[2\text{ }m{{s}^{-1}}.\] What is the reflected frequency as heard by the driver and the number of beats produced per second?(Velocity of sound\[=350\,m{{s}^{-1}}\])

    A)  708 Hz, 8                   

    B)  692 Hz, 8       

    C)       700 Hz, 0        

    D)      696 Hz, 4                   

    Correct Answer: A

    Solution :

    The frequency, of the reflected sound as heard by the driver \[=v'=v\times \frac{v+u}{v-u}=7000\times \frac{350+2}{350-2}=708\,Hz.\] Number of beats heard per second \[=v'-v=708-700=8.\] Hence, the correction option is (a).


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