two pints A and B on the surface of the earth are at the same longitude and 60o
ID: 1675858 • Letter: T
Question
two pints A and B on the surface of the earth are at the same longitude and 60o apart in latitude suppose that an earth quake at point A creates a P wave that reaches point B by traveling straight through the body of the earth at constant speed of 7.80 km / s the earth quake also radiates a Rayleigh wave which travels across the surface of the earth in an analogous way to a surface wave on water at 4.50 km / s (a) which of these two sesmic waves arrives at B first (b) what is the time difference between the arrivals of the two waves at B take the radius of the earth to be 6370 kmExplanation / Answer
(a)
from the given problem we can see that thelongitudinal wave travels a shorter distance and is moving fasterso it will
arrive at point B first
(b)
the wave that travels through the earth musttravel a distance of
2 R sin30o = 2 (6.37 x 106m) sin30o
= ........ m
the speed must be 7800 m / s
the time will be
t = 6.37 x 106 m / 7800 m / s
the wave that travels at the earth'ssurface must travel a distance of
s = R
= R ( / 3) rad
= (6.37 x 106 m)
= ........ m
the speed must be 4500 m / s
the time will be
t = 6.37 x 106 m / 4500 m / s
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