Explanation: \(\vec{r} = t\hat{i} + (t^2 + 1)\hat{j} + 2t\hat{k}\)
\(\implies \frac{d\vec{r}}{dt} = 2t\hat{i} + 2t\hat{j} + 2\hat{k}\)
\(\implies \frac{d^2\vec{r}}{dt^2} = 2\hat{i} + 2\hat{j}\)
\(\therefore |\vec{a}| = \sqrt{2^2 + 2^2} = 2\sqrt{2}\)
\(\text{Ans. (B)}\)