Earthquakes generate sound waves inside the earth. Unlike a gas, the earth can experience both transverse (S) and longitudinal (P) sound waves. Typically the speed of S wave is about 4.0 km s–1, and that of P wave is 8.0 km s–1. A seismograph records P and S waves from an earthquake. The first P wave arrives 4 min before the first S wave. Assuming the waves travel in straight line, at what distance does the earthquake occur?11th physics , chapter-15
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let V1 is the speed of p-wave = 8km/s
and V2 is the speed of s-wave=4km/s
t1 is the time taken by p-wave to reach the recorder.
t2 is the time taken by s-wave to reach the recorder.
because both travel same distance from the centre to the detector,
V1.t1 = V2t2
8.t1 = 4t2
2t1=t2--------------------------------(1)
given, t2 - t1 = 4min -------------------------------(2)
from eqns (1) and (2)
t1 = 4min and t2 = 8min
the distance b/w detector and centre is = 8*10^3*(4*240)m
= 1920 * 10^3 m
=1920 km
and V2 is the speed of s-wave=4km/s
t1 is the time taken by p-wave to reach the recorder.
t2 is the time taken by s-wave to reach the recorder.
because both travel same distance from the centre to the detector,
V1.t1 = V2t2
8.t1 = 4t2
2t1=t2--------------------------------(1)
given, t2 - t1 = 4min -------------------------------(2)
from eqns (1) and (2)
t1 = 4min and t2 = 8min
the distance b/w detector and centre is = 8*10^3*(4*240)m
= 1920 * 10^3 m
=1920 km
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