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14. waves and sound — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics14. waves and sound1 Mark
MCQ
An observer moves towards a stationary source of sound of frequency $n$. The apparent frequency heard by him is $2n$. If the velocity of sound in air is  $332\, m/sec, $ then the velocity of the observer is .... $m/sec$
  • A
    $166$
  • B
    $664$
  • ✓
    $332$
  • D
    $1328$
✓

Answer

Correct option: C.
$332$
c
(c) $n' = n\,\left( {\frac{{v + {v_O}}}{v}} \right) $

$\Rightarrow 2n = n\,\left( {\frac{{v + {v_0}}}{v}} \right) $

$\Rightarrow \frac{{v + {v_0}}}{v} = 2$

$ \Rightarrow $ ${v_O} = v = 332 \,m/sec$

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