a water wave has frequency 0.40 Hz and wavelength 2.0m. Its speed is

V = L*f = 2 * 0.4 = 0.8 m/s.

To determine the speed of a water wave, you can use the equation:

Speed = Frequency × Wavelength

Given that the frequency of the water wave is 0.40 Hz and the wavelength is 2.0 m, you can substitute these values into the equation:

Speed = 0.40 Hz × 2.0 m

Multiply the frequency (0.40 Hz) by the wavelength (2.0 m):

Speed = 0.80 m/s

Therefore, the speed of the water wave is 0.80 m/s.