Answer to No 10.
Wavelength(m) = Velocity(m/s) divide by frequency of the wavelength(Hz).
i.e 6 divide by 0.5 = 12m
Therefore wavelength = 12m
Answer to No 11.
Speed of wave or wave speed = wavelength x frequency of the Wavelength
New Wavelength gotten is = 12
Frequency = 0.5hz
Therefor Wavespeed= 12 x 0.5 = 6nm/s
Answer to No 12
They want you to find the new wave frequency to be used as wave crest and wave frequency = wave speed divide by wavelength
F= 6 divide by 12
F = 1/2 or 0.5sec
There 0.5sec would pass between wave crest