A particle moves along positive branch of the curve $y=x / 2$; where $x=t^{3} / 3, x$ and $y$ are measured in metres and $t$ in seconds, then
(a) the velocity of particle at $t=1 \mathrm{~s}$ is $\hat{i}+(1 / 2) \hat{j}$
(b) the velocity of particle at $t=1 \mathrm{~s}$ is $(1 / 2) \hat{i} \mid \hat{j}$
(c) the acecleration of particle at $t=2 \mathrm{~s}$ is $2 \hat{i}+\hat{j}$
(d) the acceleration of particle at $t=2 \mathrm{~s}$ is $\hat{i}$ ? $2 \hat{j}$