Final answer:
The frequency of the wave causing a leaf to oscillate two complete cycles each second is 2 Hz. Thus, the leaf oscillates at a frequency that would cause a bird sitting on the water to move up and down a distance of 0.4 m with every wave, repeating this motion twice per second.
Step-by-step explanation:
The student's question about the floating leaf oscillating up and down due to a water wave involves concepts related to the frequency of waves. Since the leaf completes two full cycles each second, the correct frequency is 2 Hz, which is option C. It is essential to understand that frequency refers to the number of complete oscillations or cycles that occur each second.
For the additional information provided about wave characteristics, knowing that if the amplitude of a wave is 0.2 m and its frequency is 2 Hz, a bird sitting on the water's surface would move up and down a total distance equal to twice the amplitude (once up and once down) per cycle. Therefore, the bird will go up and down a distance of 0.4 m during each cycle, and since the frequency is 2 Hz, it will do this twice every second.