A ball is projected with velocity (u) at an anle ` alpha` with horizontal plane. What is its speed when it makes an angle ` theta` whith the horizontal plane ?

Explanation

Let (v) be the velocityoa ball at an instant, when it makes and angle ` beta` with the horizontal. The horizontal component velocity of the ball
` = v cos beta`
Initial horizontal component velocity of ball
` = v cos beta`
In angular grojection of a projectile, the horizontal component velocity remains unchanged, hence `v cos beta =u cos alpha`
or `v=u cos alpha //cos beta`.