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Earthquakes generate sound waves inside the earth.Unlike a gas, theearth can experience both transverse (S) and longitudinal ( P ) sound waves.Typically the speed of S waveis about 4.0 km s^(-1) .and that of P is 8.0 km s^(-1) .Aseismograph records P and S waves from an earthquake.The first P wavearrives 4 min before the first wave.Assuming the waves travel in straight line, at what distance does the earthquake occur ? |
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Answer» Solution :Let`v_(1),v_(2)` be the VELOCITY of S WAVES & P waves &`t_(1),t_(2)` be the time TAKEN by these waves to travel to the position ofseismograph . If l is the distanceof occurrence of earthquake from the seismograph , then `l= v_(1)t_(1) = v_(2)t_(2)`...(i) now `v_(1) = 4km //s `& ` v_(2)= 8 km//s ` `:. 4t_(1) = 8 t_(2) ` (or) ` t_(1) = 2 t_(2)`...(II) Also `t_(1) - t_(2) = `4 min = 240s using (ii) `, 2t_(2) - t_(2) =240s, t_(2)= 240s ` `t_(1)=2t_(2)=2 xx 240 = 480 s` Now from (i) `l= v_(1) t_(1) = 4 xx 480 = 1920 km` Hence earthquake occurs1920 km away from theseismograph. |
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