Q172 / 180 · KCET 2008 · Physics

With what velocity should an observer approach a stationary sound source, so that the apparent frequency of sound should appear double the actual frequency? ( is velocity of sound).

  • A
    $\frac{v}{2}$
  • B
    $3 \mathrm{v}$
  • C
    $2 \mathrm{~V}$
  • Correct answer
    D
    None of these

Solution

By using $$ \begin{gathered} v^{\prime}=v\left[\frac{v-v_{0}}{v-v_{s}}\right] \\ 2 v=v\left[\frac{v-v_{0}}{v-0}\right] \end{gathered} $$ $\Rightarrow \quad \mathrm{v}_{\mathrm{o}}=-\mathrm{v} .$ Negative sign indicates that observer is moving opposite to the direction of velocity of sound.

Hence, the correct answer is option: 'D'.

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