The position vector of a particle is given as $\vec{r}=\left(t^{2}-4 t+6\right) \hat{i}+\left(t^{2}\right) \hat{j}$. The time after which the velocity vector and acceleration vector becomes perpendicular to each other is equal to

(A) $1 \mathrm{sec}$

(B) $2 \mathrm{sec}$

(C) $1,5 \mathrm{sec}$

(D) not possible