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

Rajasthan BoardEnglish MediumSTD 11 SciencePhysics14. waves and sound1 Mark
MCQ
A source and an observer approach each other with same velocity $50 m/s$. If the apparent frequency is $435 \,s^{-1}$, then the real frequency is .... $s^{-1}$
  • ✓
    $320$
  • B
    $360$
  • C
    $390$
  • D
    $420$
✓

Answer

Correct option: A.
$320$
a
(a) $n' = n\left[ {\frac{{v + {v_O}}}{{v - {v_S}}}} \right];$

Here $v = 332$m/s and ${v_0} = {v_s} = 50 m/s$

$ \Rightarrow $$435 = n\left[ {\frac{{332 + 50}}{{332 - 50}}} \right]$

$\Rightarrow n = 321.12\,\,se{c^{ - 1}} \approx 320\,se{c^{-1}}$

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