While watching ocean waves at the dock of the bay, Otis notices that 10 waves pass beneath him in 30 seconds. he also notices that the crests of successive waves exactly coincide with the posts that are 5 meters apart. What is the period of the waves

3 s

Explanation:

Since he observes 10 waves after 30 seconds then it means for every 1 wave it takes 30/10 = 3 seconds to appear. This is the period of the waves. Also since the waves are 5 m apart, that is the wavelength ie wavelength is 5 m. Note that frequency is reciprocal of period hence frequency is 1/3 = 0.33 Hz