A link $OB$ is rotating with a constant angular velocity of $2$ $rad$/$s$ in counter clockwise direction and a block is sliding radially outward on it with an uniform velocity of $0.75$ $m$/$s$ with respect to the rod, as shown in the figure below. If $OA$ = $1$ $m$, the magnitude of the absolute acceleration of the block at location $A$ in $m$/$s^2$ is

1. $3$
2. $4$
3. $5$
4. $6$