Can anyone help me out with this physics problem please?
Oct 29, 2009
in
Earthquake Questions
When an earthquake occurs, two types of sound waves are generated and travel through the earth. The primary, or P, wave has a speed of about 9.0 km/s and the secondary, or S, wave has a speed of about 4.5 km/s. A seismograph, located some distance away, records the arrival of the P wave and then, 140 s later, records the arrival of the S wave. Assuming that the waves travel in a straight line, how far is the seismograph from the earthquake?
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2 comments
kuiperbelt2003 on October 29, 2009 at 6:59 pm
the earthquake waves travel a distance D to the seismograph; the P wave can be described via:
D = speed of P wave x time of P wave travel or
D=9000m/s x t1
for the S wave, we have the same distance, and
D=4500xt2 where we know t2=t1+140
so we have
9000t1=4500t2 = 4500(t1+140)
9000t1=4500t1+630000
4500t1=630000=>t1=140s
if the P wave is traveling 9000m/s for 140s, the earthquake occured D=9000m/s x 140s = 1,260,000 m or 1260 km away
we could have figured this result by realizing the P wave travels twice as fast as the S wave, so that the S wave would take twice as long as the P wave to arrive
Chris T. on October 29, 2009 at 6:59 pm
Just from the re-e-eally basic physics that i know, and this is probably wrong, but I’m guessing 45 km, because the standard rate of acceleration is 10 m/s, so assuming that it decelerates at that rate it would have to catch the last of wave S, and 4.5 times 10 is 45. Again, probably wrong though.