How long does it take for a ball freely falling from a height of 30m to travel 20m?

How long does it take for a ball freely falling from a height of 30m to travel 20m? What is the speed of the ball at this point in time?

Data: the ball fell freely (V0 (initial velocity of the ball) = 0 m / s); h (height from which the ball started falling) = 30 m; S (path the ball must travel) = 20 m.

Constants: g (acceleration of gravity) ≈ 10 m / s2 = a (acceleration of the ball).

1) Walking the path 20 m: S = g * t ^ 2/2 = a * t ^ 2/2, whence t = √ (2S / g) = √ (2 * 20/10) = 2 s.

2) The speed of the ball at a height of 20 m: V = V0 + a * t = g * t = 10 * 2 = 20 m / s.

Answer: The ball will travel 20 m in 2 s and its speed at this time will be 20 m / s.