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A worker knocks on one end of a long steel rail.

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

A worker knocks on one end of a long steel rail. A friend puts an ear to the other end, $680\ \text{m}$ away. The sound travels through the rail at $5100\ \text{m/s}$ and through the air at $340\ \text{m/s}$ . After how long does the friend hear each sound, and what is the gap between them?

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

Have you tried it?

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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← A boy stands 612 m from a starter who fires a gun.The temperature of the air is 40 °C. Use v = (331 + 0.6T) m/s, with T in °C, to find the speed of… →

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