WAEC Physics 2020 Paper

Concept:When waves move from deep water to shallow water, their frequency remains constant, while their speed and wavelength change.Explanation:For the wave in deep water, the frequency is:$$f = \frac{v}{\lambda} = \frac{18}{3.6} = 5\ \text{Hz}$$This frequency remains the same in shallow water.In shallow water, the wavelength is $\lambda = 2.0\ \mathrm{cm}$.So, the speed in shallow water is:$$v = f \lambda = 5 \times 2.0 = 10.0\ \mathrm{cm\,s}^{-1}$$Answer:The speed of the waves in shallow water is $10.0\ \mathrm{cm\,s}^{-1}$.Therefore, the correct option is C.