Wave Equation

I'm stuck on this question. I know there is a reflection wave on the soft boundary (the ring) and it's not inverted and there is no phase change either. 

Suppose $g$ and $h$ have compact support and $u\in C^2(\mathbb{R}\times [0,\infty))$ solves the wave equation and $u=g$, $u_t=h$ on $\mathbb{R}\times \{t=0\}$. The kinetic energy of the wave is and th...

(Equipartition of energy). Let $u \in C^2(\R \times [0,\infty))$ solve the initial-value problem for the wave equation in one dimension: \begin{cases} u_{tt}-u_{xx}=0 & \text{ in } \R \times (0,...