wave equation for rotational symmetric initial value

i have no idea how to solve the following:

Solve the wave equation in $\mathbb{R}^3$ with rotationalsymmetric initial value $u_0(x) = \phi(|x|), u_1(x) = 0$. How looks the solution, if $u_0(x)$ is the characteristic function of the sphere $S_R(0), R > 0$?

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