A particle is projected in air at some angle to the horizontal, moves along parabola as shown in figure where x and y indicate horizontal and vertical directions, respectively . Shown in the diagram, direction of velocity and acceleration at points A, B and C.

Explanation

Consider the adjacent diagram in which a particle is projected at an angle `theta`.

`v_(x)`=Horizontal component of velocity = v `cos theta`=constant.
`v_(y)` = Vertical component of velocity `=v sin theta`
Velocity will always be tangential to the curve in the direction of motion and acceleration is always vertically downward and is equal to g (acceleration due to gravity).