The velocity of the transverse waves produced by an earthquake is 8.9 km/s, and that of the longitudinal waves is 5.1 km/s. A seismograph records the arrival of the transverse waves 68 s before the arrival of the longitudinal waves. How far away is the earthquake?

Answer: The distance is 723.4km

Explanation:

The velocity of the transverse waves is 8.9km/s

The velocity of the longitudinal wave is 5.1 km/s

The transverse one reaches 68 seconds before the longitudinal.

if the distance is X, we know that:

X / (9.8km/s) = T1

X / (5.1km/s) = T2

T2 = T1 + 68s

Where T1 and T2 are the time that each wave needs to reach the sesmograph.

We replace the third equation into the second and get:

X / (9.8km/s) = T1

X / (5.1km/s) = T1 + 68s

Now, we can replace T1 from the first equation into the second one:

X / (5.1km/s) = X / (9.8km/s) + 68s

Now we can solve it for X and find the distance.

X / (5.1km/s) - X / (9.8km/s) = 68s

X (1 / (5.1km/s) - 1 / (9.8km/s)) = X*0.094s/km = 68s

X = 68s/0.094s/km = 723.4 km