Earthquakes generate sound waves inside the earth. The earth can experience both transverse(S) and longitudinal(P) sound waves. Typically the speed of S is abt. 4km/s and that of P is 8 km/s. A seismograph records P and S waves from an earthquake. The first P wave arrives 4 min. before the first S wave. At what distance does the earthquake occur?

Let 1st "P" wave reach @ time = t

=> Dist. = Speed*Time

=> d = 8t ....(1)

For "S" wave....time = t + 240 seconds

=> d = 4 (t +240) ......(2)

Solve Eqns (1) & (2)....

v get ....d = 1920 km

Tht shud b the required distance....