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RAJASTHAN PMT Rajasthan - PMT Solved Paper-2004

  • question_answer
    Two sound sources \[{{S}_{1}}\] and\[{{S}_{2}}\]of frequencies 324 Hz and 320 Hz are placed at certain separation. An observer is moving away from\[{{S}_{1}}\] and towards \[{{S}_{2}}\] on line joining them. If he hears no beats then speed of observer is (\[\upsilon \]= 344m/sec):

    A)  20 m/s

    B)         10 m/s

    C)  5 m/s                   

    D)         2.1 m/s

    Correct Answer: D

    Solution :

    Number of beats\[\Delta n={{n}_{1}}-{{n}_{2}}\] For no beats observed, \[{{n}_{1}}-{{n}_{2}}=0\] \[\therefore \]  \[\left( \frac{\upsilon -{{\upsilon }_{0}}}{\upsilon } \right)\times 324-\left( \frac{\upsilon +{{\upsilon }_{0}}}{\upsilon } \right)\times 320=0\] where, \[{{\upsilon }_{0}}=\]speed of observer and \[\upsilon =\]344 m/s On solving, \[{{\upsilon }_{0}}=2.1\] m/sec


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