The principle of superposition: $x$-motion is independent of $y$-motion
 $x$-component variable $y$-component $x$ displacement, $\vec{r}$ $y$ $V_x$ velocity, $\vec{V}$ $V_y$ $V_{0x}$ initial velocity, $\vec{V_0}$ $V_{0y}$ $a_x$ acceleration, $\vec{a}$ $a_y$ time, $t$ $\begin{eqnarray*} V_x & = & V_{0x}+a_xt \\ x & = & \overline{V_x}t={1\over2}(V_x+V_{0x})\>t \\ x & = & V_{0x}t+{1\over2}a_xt^2 \\ V_y^2 & = & V_{0y}^2+2a_y y \end{eqnarray*}$ equationsofkinematics $\begin{eqnarray*} V_y & = & V_{0y}+a_yt \\ y & = & \overline{V_y}t={1\over2}(V_y+V_{0y})\>t \\ y & = & V_{0y}t+{1\over2}a_yt^2 \\ V_x^2 & = & V_{0x}^2+2a_x x \end{eqnarray*}$