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STD 11 - 14. waves and sound — JEE STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceJEESTD 11 - 14. waves and sound4 Marks
MCQ
The frequency changes by $10\%$ as a sound source approaches a stationary observer with constant speed $v_s$. What would be the percentage change in frequency as the source recedes the observer with the same speed. ... $\%$ Given that $v_s < v$. ($v =$ speed of sound in air)
  • A
    $14.3$
  • B
    $20$
  • C
    $10.0$
  • ✓
    $8.5$
✓

Answer

Correct option: D.
$8.5$
d
as per given situation,

$\frac{\nu^{\prime}}{\nu}=\frac{V}{V-V_{s}}=1.1$

$V_{s}=\frac{1}{11} \times V$

in the second condition,

$\frac{\nu^{\prime}}{\nu}=\frac{V}{V+V_{s}}=\frac{V}{V+(1 / 11) \times V}=\frac{11}{12}$

$\frac{\nu^{\prime}}{\nu} \times 100=\frac{11}{12} \times 100=91.66^{\circ} \%$

hence change is around $8.5 \%$

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