The body is thrown vertically downward at a speed of 20 m / s, which is equal to the speed of the body 1 s after the throw.

V0 = 20 m / s.
g = 9.8 m / s ^ 2.
t = 1 s.
V -?
The body will be in a state of free fall, due to the action of only gravity.
It will move with constant gravitational acceleration g.
Let’s write down the formulas for acceleration: g = (V -V0) / t.
V -V0 = g * t.
V = V0 + g * t.
V = 20 m / s + 9.8 m / s ^ 2 * 1 s = 29.8 m / s.
Answer: after 1 s from the moment of throwing, the body will have a velocity V = 29.8 m / s.