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JEE Main & Advanced Sample Paper JEE Main - Mock Test - 6

  • question_answer
    A sound wave of wavelength 'k travels towards the right horizontally with a velocity V. It strikes and reflects from a vertical plane surface, traveling at a speed v towards the left. The number of crests striking in a time interval of three seconds on the wall is

    A) \[\frac{3(V+v)}{\lambda }\]

    B) \[\frac{3(V-v)}{\lambda }\]

    C) \[\frac{(V+v)}{3\lambda }\]       

    D) \[\frac{(V-v)}{3\lambda }\]

    Correct Answer: A

    Solution :

    [a] The relative velocity of sound waves with respect to the walls is\[V+v\]. Hence, the apparent frequency of the waves striking the surface of the wall is \[\frac{(V+v)}{\lambda }\] . The number of positive crests striking per second is the same as frequency. In three seconds, the number is \[[3\,(V+v)]/\lambda \].


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