When a piece is thrown straight up, its height is [[$ h $]] measured from the starting level [[$ h = v_0 t - \displaystyle\frac {1} {2} g t^2 $]], where [[$ v_0 $]] is the initial speed, [[$ t $]] is time and [[$ g $]] is the value of gravitational acceleration ([[$ 9.81 $]] m/s[[$ ^2 $]]).

The ball is thrown up at an initial speed of [[$ 8,0 \;\text {m/s} $]]. Calculate the time [[$ t $]] when the height of the ball is [[$ 0 \;\text {m} $]].

Answer: The time is [[$ t = $]] s or [[$ t = $]] s.