A flash of lightning is seen 2 s before thunder is heard. How far away is the cloud? Take sound speed 332 m s⁻¹.

Solution & explanation

1. Given delay 2 s and sound speed 332 m s⁻¹. Treat light travel time as negligible over this distance.

2. This is one-way sound travel, not an echo. Do not divide by two.

3. Use distance = speed × time.

   $$d=t\times v$$

4. Insert values.

   $$d=332\times 2$$

5. Multiply.

   $$d=664$$

6. The distance is measured in metres.

d = 664 m