When an object is thrown in gravitational field of the Earth, it moves with constant horizontal velocity and constant vertical acceleration. Such a two dimensional motion is called a projectile motion and such an object is called a projectile.
For example, when we kick a football, it performs projectile motion if air resistance is neglected. A projectile has motion along horizontal path with uniform velocity.
A projectile has motion along vertical path under gravity with uniform acceleration equal to ' $g$ '.
Suppose that the projectile is launched with velocity $\vec{v}_{0}$ that makes an angle $\theta_{0}$ with the $\mathrm{X}$-axis as show in figure.
$\mathrm{g}$ acts on the body along ' $\mathrm{Y}$ ' axis and in opposite direction
The acceleration ' $a$ ' is given by
$\therefore \vec{a}=-\mathrm{g} \hat{j}$
here $a_{x}=0, a_{y}=-g$
The velocity $\vec{v}_{0}$ can be divided into two components,
$v_{\mathrm{o} x}=v_{\mathrm{o}} \cos \theta_{\mathrm{o}}$
$v_{\mathrm{oy}}=v_{\mathrm{o}} \sin \theta_{\mathrm{o}}$
If we take the initial position to be the origin of the coordinate system, the coordinates of the point of projection would be :
$x_{0}=0$, and $y_{0}=0$