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J & K CET Medical J & K - CET Medical Solved Paper-2006

  • question_answer
    A motor car is approaching towards a crossing with a velocity of 72 km/h. The frequency of sound of its horn as heard by a policeman standing on the crossing is 260 Hz. The frequency of horn is:

    A)  200 Hz                                 

    B)  244 Hz

    C)  150 Hz                                 

    D)  80 Hz

    Correct Answer: B

    Solution :

                     From Doppler's effect, perceived frequency is \[n'=n\left( \frac{v-{{v}_{0}}}{v-{{v}_{s}}} \right)\] \[{{v}_{s}}=72\,km/h=\frac{72\times 1000}{60\times 60}=20\,m/s\] \[{{v}_{0}}=0,\,v=332m/s,\,n'=260\,Hz\]                 \[260=n\left( \frac{332}{332-20} \right)\] \[\Rightarrow \]               \[n=\frac{260-312}{332}=244\,Hz\]


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