Describe a method for measuring the speed of sound in air, in the laboratory. What measurements are made, and how is the speed of sound calculated from them?

To measure the length of a long metal rod, engineers send a pulse of sound into one end of it. The sound travels to the other end and is reflected back. The engineers detect this echo and determine the time taken for the sound to travel from one end of the rod to the other.

When making measurements on the steel rod of length $400 \mathrm{m}$, they find that the echo returns $0.16 \mathrm{s}$ after the initial pulse. What is the speed of sound in steel, in $\mathrm{m} {\mathrm{s}}^{-1}$

The boat is sailing away from the shore. The depth of water increases uniformly with distance from the shore.

Copy the axes shown in the diagram. Sketch a graph that shows how the time interval to hear the echo might change as the distance from the shore changes.

A teacher is trying to find an unusual way to measure the speed of sound using an echo method. She has a firework, which will make a loud bang at ground level when ignited. She also has a stopwatch and a tape to measure.

To obtain an echo, she needs a suitable reflector. Suggest something that she could use as a reflector.