Answer
The energy density is $~~0.11~J/m^3$
Work Step by Step
We can find the electric field near the surface of the sphere:
$E = \frac{V}{r} = \frac{8000~V}{0.050~m} = 160,000~V/m$
We can find the energy density:
$u = \frac{1}{2}\epsilon_0~E^2$
$u = (\frac{1}{2})(8.854\times 10^{-12}~C/V~m)(1.6\times 10^5~V/m)^2$
$u = 0.11~J/m^3$
The energy density is $~~0.11~J/m^3$
