Wave Motion

1. Dec 12, 2009

laxboi33

1. The problem statement, all variables and given/known data

Assume that P and S (Primary and Secondary) waves from an earthquake with a focus near the Earth's surface travel through the Earth at nearly constant but different average speeds. A monitoring station that is 1000 km from the epicenter detected the S wave to arrive at 42 seconds after the arrival of the P wave. If the P wave has an average speed of 8.0 km/s, what is the average speed of the S wave?

2. Relevant equations
v = Lambda/T
or
v= Lambda * f

3. The attempt at a solution

The period of the wave should be 42 seconds which would make the frequency : 1/42 or .0238

If the velocity is 8.0 km/s then to find Lambda you would have to:
8 = lambda * .0238 which makes Lambda 336.13

Where I get confused is when I multiply, 336.13 * .023, I get an answer of 8 again which would be the velocity of the primary wave. I assume that there is a new frequency that needs to be used in the equation, but I can't seem to figure it out. Any help would be great. Thanks.

2. Dec 12, 2009

ideasrule

This has nothing to do with frequencies and wavelengths and everything to do with speeds and distances. Replace the waves with cars and see what you get.