Evaluate $\iint_D (x^2+y^2)^{3/2}dxdy$

Using polar coordinates (note that $D$ is a disk of radius 2):  
\[\iint_D (x^2+y^2)^{3/2}dxdy=\int_0^{2\pi}\int_0^{2}(r^2)^{3/2}rdrd\theta=\int_0^{2\pi}\int_0^{2} r^4 dr d\theta\]
\[=\int_0^{2\pi}\frac{r^{5}}{5}|_0^{2} d\theta=\int_0^{2\pi} \frac{2^5}{5}d\theta =\frac{32}{5}\int_0^{2\pi} d\theta=\frac{32}{5} \times 2\pi=\frac{64 \pi}{5}.\]