Question

Crests of an ocean wave pass a pier every 10.0 s. if the waves are moving at 5.6 m/s, what is the wavelength of the ocean waves?

Answer 1

Every 10.0 seconds, a crest of the wave passes the pier. This means that the period of the wave is exactly 10.0 s:
$T=10.0 s$
which means that the frequency of the wave is
$f= \frac{1}{T}= \frac{1}{10.0 s}=0.1 Hz$

The wavelength of a wave is related to its frequency by the relationship
$\lambda= \frac{v}{f}$
where v is the speed of the wave.
In this problem, v=5.6 m/s; if we use the previous formula, we find the wavelength of the wave:
$\lambda= \frac{5.6 m/s}{0.1 Hz}=56 m$