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JEE Main & Advanced Physics Wave Mechanics Question Bank Self Evaluation Test - Waves

  • question_answer
    A car is moving towards a high cliff. The car driver sounds a horn of frequency \[f\]. The reflected sound heard by the driver has as frequency \[2f\]. If v be the velocity of sound, then the velocity of the car, in the same velocity units, will be

    A)  \[v/2\]

    B)  \[v/\sqrt{2}\]

    C) \[v/3\]  

    D) \[v/4\]

    Correct Answer: C

    Solution :

    [c] Let f? be the frequency of sound heard by cliff \[\therefore \,f'=\frac{vf}{v-{{v}_{c}}}\]                 ....... (1) Now for the reflected wave cliff, acts as a source \[\therefore \,\,2f'=\frac{f'(v+{{v}_{c}})}{v}\]           ...... (2) \[2f=\frac{(v+{{v}_{c}})f}{v-{{v}_{c}}}\Rightarrow 2v-2\,\,\,\,\,{{v}_{c}}=v+{{v}_{c}}\] or \[\frac{v}{3}={{v}_{c}}\]


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