Earthquake Waves: Calculate Distance from Station

[maff is tuff]

Homework Statement

Earthquakes produce several types of shock waves. The best known are the P-waves (P for primary or pressure) and the S-waves (S for secondary or shear). In the Earth's crust, P-waves travel at around 6.40 km/s while S-waves move at about 3.60 km/s. (The actual speeds vary with the type of material the waves are going through.) The time delay between the arrival of these two types of waves at a seismic recording station tells geologists how far away the earthquake that produced the waves occurred.

If the time delay at a seismic station is 41.0 s, how far from that station did the earthquake occur?

Homework Equations

The Attempt at a Solution

This one is really stumping me. Maybe I am missing something big. My givens are: I know two different velocities (6.4 km/h and 3.6km/h) and I know a time delay of 41 seconds. So that means that the first wave gets there 41 seconds before the second wave does. I don't really know what to do with this information. The only thing I could think of is using the formula: v^2 = v0^2 + 2a(x-x0) but since I don't know "a" I could maybe plug in (v-v0)t for "a"? I really don't know where to start. Only thing I can think of that I know I'll eventually have to do is convert 41s into .01139 hours. Can I come of with an acceleration by taking the difference of the velocities and dividing by the .01139h? Can anybody get me started? Thanks!

 

[ehild]

The problem gives the velocities in km/s, and the time is in seconds, no need to convert the velocities to km/h.
The velocities are constant, there is no acceleration.

Forget about earthquakes, try to think of this more familiar problem: You and your sister start from home and go to the school. You walk with 6.4 km/h and your sister walks with 3.6 km/h. You arrive a quarter of hour earlier than your sister. How far is the school from your home?

ehild

 

[maff is tuff]

Ok thanks I don't know why I converted it. Yeah thanks for the explanation; it helped.