A solid metal ball is thrown directly downward, with an initial speed of 8.55 m/s, from the top of a structure at a height of 30.6 m. How much time (in s) does it take before striking the ground?

1.8 sec

Explanation:

Consider the motion of the ball in downward direction as positive

v₀ = initial speed of the metal ball = 8.55 m/s

a = acceleration of the ball = 9.8 m/s²

y = vertical displacement of the ball = height of the structure = 30.6 m

t = time taken by the ball to hit the ground

Using the equation

y = v₀ t + (0.5) a t²

30.6 = (8.55) t + (0.5) (9.8) t²

t = 1.8 sec