A marine researcher is using a coastal model wave tank to study the propagation of surface waves.
The researcher measures the time taken for 20 wave crests to pass a fixed vertical piling. They repeat this measurement three times and calculate a mean. State the advantage of repeating measurements and calculating a mean.
The researcher's three measurements for the time taken for 20 wave crests to pass the piling are: 7.8 s,8.4 s,8.1 s7.8\text{ s}, \quad 8.4\text{ s}, \quad 8.1\text{ s}7.8 s,8.4 s,8.1 s Calculate the mean frequency of the wave. Give your final answer to 2 significant figures.
In another part of the investigation, the researcher wants to determine the speed of the waves. The researcher is unable to measure the wavelength of the waves directly. Explain how the researcher could determine the speed of the waves.