SOLUTION: Hello, Here is the question I need to solve to begin with An earthquake emits primary waves moving at 8.0 Km/s and seconday waves moving at 5.0 km/s. How far from the epi-center

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Question 11610: Hello, Here is the question I need to solve to begin with
An earthquake emits primary waves moving at 8.0 Km/s and seconday waves moving at 5.0 km/s. How far from the epi-center of the earthquake is the seismic station if the two waves arrive at the station 2.0 min apart.
What I could figure out (I think)
I was converting time to seconds
2 min = 60x2=120 min
and converting km/s to ft/s
8.0km/s x 1000 m =8000m
8000m x 3.281 = 26248 ft/s
5.0km/s x 1000 m = 5000 m
5000m x 3.281 ft = 16405 ft/s
I was also trying calculations with d=rt where d= distance r= stands for rate of speed and t= time.
Thank you so much to any help or direction you can point me in!

Answer by Earlsdon(6294) About Me  (Show Source):
You can put this solution on YOUR website!
First, I don't see any need to convert Km to feet. Ok to convert 2 minutes to 120 seconds.
For the primary wave:
d1+=+%28r1%29t1
d1+=+%2880%29t1
For the secondary wave:
d2+=+%28r2%29t2
d2+=+%285%29%28t1%2B120%29
But, d1 = d2, so:
80t1+=+5%28t1%2B120%29 Simplify and solve for t1.
80t1+=+5t1+%2B+600 Subtract 5t1 from both sides.
75t1+=+600 Divide both sides by 75.
t1+=+8seconds. Substitute this into d1+=+80t1 and solve for d1.
d1+=+80%288%29
d1+=+640 Km.
Check:
d2+=+r2%28t1%2B120%29
d2+=+5%288%2B120%29
d2+=+5%28128%29
d2+=+640Km.