Is it possible to derive velocity vector form position vector without unknown such as: position vector of A = (0.8)i + (1.2)j?
If you only have a general postion vector that describes the path of the object, then it's impossible to derive the velocity vector. Here I try to demonstrate it:
Since the point masses are dimensionless, we can consider two different point masses at the exact same location. Point mass $m_1$ moves with velocity $v_1$ so the point mass $m_2$ with $v_2$, those masses share the same location but move with different speeds.