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  3. RAJASTHAN ­ PET

RAJASTHAN ­ PET Rajasthan PET Solved Paper-2002

  • question_answer
    A body is walking away from a wall towards an observer at a speed of 2 m/s and blows a whistle whose frequency is 680 Hz. The number of beats heard by the observed per second is (velocity of sound in air = 340 m/s)

    A)  zero            

    B)  2

    C)  8               

    D)  4

    Correct Answer: D

    Solution :

     Observer will listen two frequencies (i) First, \[{{n}_{1}}=680\left( \frac{340}{340-1} \right)\] (ii) Second, \[{{n}_{2}}=680\left( \frac{340}{340+1} \right)\] Then, \[{{n}_{1}}-{{n}_{2}}=4\]


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