The body is thrown vertically downward at a speed of 5m / s from a height of 20m.

The body is thrown vertically downward at a speed of 5m / s from a height of 20m. Determine the time of falling of the body to the ground and the speed of the body at the moment of falling.

Body path when falling:
S = V0 * t + a * t² / 2, where S is the height of the fall (S = 20 m), V0 is the initial velocity (V0 = 5 m / s), t is the fall time, and is the acceleration with which the body falls (a = g = 10 m / s²).
20 = 5 * t + 10 * t² / 2.
5 * t² + 5 * t – 20 = 0.
t² + t – 5 = 0.
D = 1² + 4 * 1 * 4 = 17.
t = (-1 + √ (21)) / (2 * 1) = 1.56 s.
Falling speed:
V = V0 + g * t = 5 + 10 * 1.56 = 20.6 m / s.
Answer: The time of the body falling is 1.56 s, the speed of the body at the moment of falling is 20.6 m / s.