Practice question · Estimate
You see a lightning flash and hear the thunder 6 seconds later. Estimate how far away the strike was, in kilometres (sound: ~340 m/s).
Estimate on a scale from 0 km (0) to 10 km (10).
Hints
- The light arrives essentially instantly; the delay is all sound travel time.
- m.
Show the answer
2 (answers within ±0.4 count)
Why
About 2 km, the origin of the "3 seconds per kilometre" storm rule. The trick works because light outruns sound by a factor of nearly a million.
Practise Sound Waves and the Doppler Effect
The app has 6 more questions on this lesson, and keeps your place in the course. Physics I is free to start.
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