A seismograph records a seismic wave that travels at $4,km/s$. If the wave takes $45$ seconds to reach the seismograph from the epicentre, how far is the epicentre from the seismograph? Show your calculation.

Step-by-step solution

1. Use the relation $\text{distance}=\text{speed}\times \text{time}$.
2. Insert the given speed $4,km/s$ and time $45,\mathrm{s}$.
3. Multiply: $4,km/s\times 45,\mathrm{s}=180,\mathrm{km}$.
4. State the distance as $180$ km.

Concept tested: Distance–time calculation for seismic waves

Published 16 October 2026 · How this solution was prepared and checked