In projectile motion, this video shows that both balls hit the ground at the same time. Why? because you substitute acceleration in the equation d=1/2 a x t(squared) with gravity which is 10m/s d= 1/2(10)x t(squared). Since there is no air resistance, then the weight of the balls don't matter and gravity is the only force acting on them, and therefore they hit the ground at the same time.