Question:
Earthquakes generate sound waves in the Earth. Unlike in a gas, there are both
transverse (S) and longitudinal (P) sound waves in a solid.
Typically, the speed of S waves is about 
and that of P
waves is 
.
A seismograph records P and S waves from an earthquake.
The first P waves arrive 
before the first S waves.
How far away did the earthquake occur?
Solution:
If the distance to the quake is X, and the time for the first S waves to
arrive is T,
then 
. Therefore, 
,
which gives 
, and hence
.