How long does it take for an arrow fired vertically upward from a bow for its speed

How long does it take for an arrow fired vertically upward from a bow for its speed to decrease 4 times? At what altitude will this happen? Boom initial speed 40 m / s

Data: V0 (initial speed of the considered boom) = 40 m / s = 4V (considered speed).

Constants: g (acceleration due to gravity) ≈ 10 m / s2.

1) Time to decrease the boom speed: V = V0 + a * t = V0 – g * t, whence we express: t = (V – V0) / (-g) = (10 – 40) / (-10) = 3 with.

2) The height at which the considered boom should be: h = V0 * t – g * t ^ 2/2 = 40 * 3 – 10 * 3 ^ 2/2 = 75 m.

Answer: The arrow speed will decrease by 4 times after 3 seconds at a height of 75 m.