Answer:
v_f = 20 m / s
Explanation:
For this exercise let's use the relationship between momentum and moment
I = Δp
F t = m v_f - m v₀
as the body starts from rest v₀ = 0
F t = m v_f
v_f = [tex]\frac{F t}{m}[/tex]
let's calculate
v_f = 4 2 / 0.4
v_f = 20 m / s