For a simple harmonic motion energy is given with:

Where k is a constant that depends on the type of the wave you are looking at and A is amplitude.
Let's calculate the energy of the wave using two different amplitudes given in the problem:

We can see that energy associated with the wave is 4 times smaller when we decrease its amplitude by half. So the answer should be C.
Explanation:
frequency =speed/wavelength
=5/0.5=10Hz
Explanation:
the force acting perpendicularly on unit area of surface
- unit=pascle .