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CMC Medical CMC-Medical VELLORE Solved Paper-2010

  • question_answer
    Two cars A and B approach a stationary observer from opposite sides as shown in figure. Observer hears no beats. If the frequency of the horn of the car B is 504 Hz, the frequency of horn of car A will be

    A)  529.2 Hz             

    B)  295.2 Hz

    C)  440.5 Hz             

    D)  259.2 Hz

    E)  None of these

    Correct Answer: A

    Solution :

                    From Dopplers effect, the apparent change in frequency of a wave that is perceived by stationary observer is\[n={{n}_{0}}\left( \frac{v}{v-{{v}_{s}}} \right)\]where,\[v\]is speed of sound. Since, observer is not hearing any beats, the apparent frequency of the two cars should be equal. \[\therefore \]  \[n=n\,\] \[504\left( \frac{v}{v-30} \right)=n\left( \frac{v}{v-15} \right)\] \[\therefore \]  \[n=\frac{(330-15)\times 504}{(330-30)}\]                    \[=\frac{315\times 504}{300}=529.2\,Hz\]


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