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BCECE Engineering BCECE Engineering Solved Paper-2014

  • question_answer
    A siren emits sound of frequency 1000 Hz, it moves away from the observer towards a cliff     with a speed of\[\text{1}0\text{ m}{{\text{s}}^{{{\text{-}}^{\text{1}}}}}\]. Then, the  frequency of sound heard by observer coming directly from the siren is

    A) less than 1000 Hz                            

    B) greater than 1000 Hz

    C) equal to 1000 Hz

    D) no sound is heard

    Correct Answer: A

    Solution :

    Sound heard \[{{f}_{1}}={{f}_{0}}\left( \frac{v}{v+{{v}_{s}}} \right)\] \[{{v}_{s}}=10m{{s}^{-1}}\] \[{{f}_{1}}=\left( \frac{330}{330\times 10} \right)\times 1000\] \[{{f}_{1}}=\frac{33}{34}\times 1000\]is less than 1000 Hz.


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