In Exercises $11-14,$ write a in the form $\mathbf{a}=a_{\mathrm{T}} \mathbf{T}+a_{\mathrm{N}} \mathbf{N}$ at the given value of $t$ without finding $\mathbf{T}$ and $\mathbf{N} .$
$$
\mathbf{r}(t)=(t \cos t) \mathbf{i}+(t \sin t) \mathbf{j}+t^{2} \mathbf{k}, \quad t=0
$$