A skipper on a boat notices wave crests passing the anchor chain every 5 seconds. the skipper estimates the distance between crests is 15 m. what is the speed of the water waves?

Because the crests occur every 5 seconds, the period is

T = 5 s.

By definition, the frequency is

f = 1/T = 1/5 = 0.2 Hz

The distance between crests is 15 m, therefore the wavelength is

λ = 15 m

By definition, the velocity, v, is

v = fλ

= (0.2 1/s) * (15 m)

= 3 m/s

Answer: 3 m/s