MCQ
An earthquake generates both transverse $(S)$ and longitudinal $(P)$ sound waves in  the earth. The speed of $S$ waves is about $4.5\,km/s$ and that of $P$ waves is about  $8.0\, km/s$. A seismograph records $P$ and $S$ waves from an earthquake. The first  $P$ wave arrives $4.0 \,min$ before the first $S$ wave. The epicenter of the  earthquake is located at a distance about ..... $km$
  • A
    $25$
  • B
    $250$
  • $2500$
  • D
    $5000$

Answer

Correct option: C.
$2500$
c
$\mathrm{t}_{\mathrm{s}}-\mathrm{t}_{\mathrm{p}}=4 \mathrm{\,min}$

$\frac{\mathrm{d}}{\mathrm{V}_{\mathrm{s}}}-\frac{\mathrm{d}}{\mathrm{V}_{\mathrm{p}}}=240 \mathrm{\,sec}$

$d\left[\frac{1}{4.5}-\frac{1}{8}\right]=240$

${\rm{d}} \simeq 2500\,{\rm{km}}$

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