Posted by Kate on Monday, April 7, 2014 at 4:36pm.
Earthquakes are essentially sound waves—called seismic waves—traveling through the earth. Because the earth is solid, it can support both longitudinal and transverse seismic waves. The speed of longitudinal waves, called P waves, is 7800m/s . Transverse waves, called S waves, travel at a slower 4400m/s . A seismograph records the two waves from a distant earthquake.
If the S wave arrives 2.1min after the P wave, how far away was the earthquake? You can assume that the waves travel in straight lines, although actual seismic waves follow more complex routes.

physics  bobpursley, Monday, April 7, 2014 at 5:56pm
dp=v*t=7800*t
ds=4400(t+2.1)
but dp=ds
set the equations equal, solve for t.
then put it in either equation, and solve for the distance.