NEET Sample Paper NEET Sample Test Paper-51

  • question_answer When the listener moves towards a stationary source with a velocity\[{{v}_{1}}\], the apparent frequency of a note emitted by the source is\[f'\]. When the listener moves away from the source with the same velocity, the apparent frequency of the note\[f'/f''\,\,=\,\,3\]. If v the velocity of sound in air, the value of \[v/{{v}_{1}}\] is-

    A) 3                                 

    B) 1 / 2

    C) 2                                 

    D) 1

    Correct Answer: C

    Solution :

    When listener moves \[f'=f\,\left( \frac{v+{{v}_{\ell }}}{v} \right)\] when moves away \[\frac{f'}{f''}\,\,=\,\,f\left( \frac{v-{{v}_{\ell }}}{v} \right)\] \[\frac{f'}{f''}\,\,=\,\,3\] \[\Rightarrow \,\,\frac{v+{{v}_{\ell }}}{v-{{v}_{\ell }}}\,\,=\,\,3\] \[\Rightarrow \,\,\,v+{{v}_{\ell }}=3v-3{{v}_{\ell }}\] \[\Rightarrow \,\,\,\,4{{v}_{\ell }}=\,\,2v\] \[\Rightarrow \,\,\,v=2{{v}_{\ell }}\] \[\frac{v}{{{v}_{\ell }}}=2\]


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