Question

A stationary boat in the ocean is experiencing waves from a storm. the waves move at 56 km/h and have a wavelength of 160 m, both typical values. the boat is at the crest of a wave. how much time elapses until the boat is first at the trough of a wave?

Answer 1

The wavelength $\lambda$ of the wave is 160 m, and this is the distance between two consecutive crests. The boat is located at a crest of the wave, this means that the first trough is located 80 meters from the boat (because the distance between a crest and a trough is half the wavelength).

The speed of the wave is 
$v=56 km/h = 15.6 m/s$
so the time the boat takes to reach the first trough is
$t= \frac{S}{v} = \frac{80 m}{15.6 m/s}=5.1 s$