A projectile is launched from a point O O\,O on a horizontal level plane with an initial velocity of v m s−1v \text{ m s}^{-1}v m s−1 at an angle α \alpha\,α to the horizontal. The projectile needs to clear a horizontal distance of s s\,s metres before it hits the ground.
By modelling the projectile as a particle and neglecting air resistance, show that
sin2α≥sgv2 \sin 2\alpha \ge \frac{sg}{v^2} sin2α≥v2sg
