1. [In this question $i$ is a horizontal unit vector and $j$ is a vertical unit vector directed upwards. Position vectors are given relative to a fixed origin $O$.]

A stone is modelled as a particle $P$ thrown from a point $O$ on the edge of a deep hole. At time $t$ seconds after being thrown, where $t\geq0$, the velocity of $P$, $vm{s}^{-1}$, is given by

$v=(0.2t)i+(4-0.75{t}^{2})j$

Find the position vector of $P$ at time $t=4$ and give an interpretation of the $j$ component of this position vector.