• # 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 / 2C) 2                                 D) 1

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