EasyPhysicsHigh School (9–10)GeneralWaves & Sound › Sound Waves and HearingNumericalBoard Exam

You see a flash of lightning, and you hear the thunder 4.5 s later…

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

You see a flash of lightning, and you hear the thunder $4.5\ \text{s}$ later. How far away was the lightning? (Speed of sound $340\ \text{m/s}$ )

Need a reminder? The key ideaShow

Speed $v = \dfrac{d}{t}$ . Sound travels at about $340\ \text{m/s}$ in air, $1500\ \text{m/s}$ in water and $5100\ \text{m/s}$ in steel. In air, $v \approx (331 + 0.6T)\ \text{m/s}$ with $T$ in $^\circ\text{C}$ .

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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