Answer:
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