RAJASTHAN PMT Rajasthan - PMT Solved Paper-2008

  • question_answer
    An observer moves towards a stationary source of sound, with a velocity one-fifth of the velocity of sound. What is the percentage increase in the apparent frequency?

    A)  Zero                                     

    B)  0.5%                    

    C)  5%                        

    D)         20%

    Correct Answer: D

    Solution :

    Given:\[{{v}_{o}}=\frac{v}{5}\Rightarrow {{v}_{o}}=\frac{320}{5}=64\,\,m/s\] When observer moves towards the stationary source, then                 \[n=\left( \frac{v+{{v}_{o}}}{v} \right)n\]                 \[n={{\left( \frac{320+64}{320} \right)}^{n}}\]                 \[n={{\left( \frac{384}{320} \right)}^{n}}\]                 \[\frac{n}{n}=\frac{384}{320}\] Hence, percentage increase                 \[\left( \frac{n-n}{n} \right)=\left( \frac{384-320}{320}\times 100 \right)%\]                 \[=\left( \frac{64}{320}\times 100 \right)%=20%\]


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