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Sound Waves — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysicsSound Waves5 Marks
Question
Figure, shows a source of sound moving along the X-axis at a speed of 22m/s continuously emitting a sound of frequency 2.0kHz which travels s in air at a speed of 330m/s. A listener Q stands on the Y-axis at a distance of 330 m from the origin. At t = 0, the source crosses the origin P.
  1. When does the sound emitted from the source at P reach the listener Q?
  2. What will be the frequency heard by the listener at this instant?
  3. Where will the source be at this instant?
✓

Answer


$\text{f}=2\text{KHz}, \text{v}=330\text{m/s},\ \text{u}=22\text{m/s}$
At t = 0, the source crosses P
  1. Time taken to reach at Q is
$\text{t}=\frac{\text{S}}{\text{v}}=\frac{330}{330}=1\text{sec}$
  1. The frequency heard by the listner is
$\text{f}'=\text{f}\Big(\frac{\text{v}}{\text{v}-\text{u}\cos\theta}\Big)$
since, $\theta=90^\circ$
$\text{f}'=2\times\Big(\frac{\text{v}}{\text{u}}\Big)=2\text{KHz}.$
  1. After 1sec, the source is at 22m from P towards right.

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