The body is thrown vertically upward with an initial speed of 30m / s in how many seconds will it be at a height of 25 meters?

To find the duration of the rise of the thrown body to the required height, we use the formula: h = S = Vn * t – g * t ^ 2/2.
Constants and variables: h – required lifting height (h = 25 m); Vн – vertical throw speed (Vн = 30 m / s); g – acceleration due to gravity (g ≈ 10 m / s2).
Let’s transform the formula into a quadratic equation: 25 = 30 * t – 10 * t ^ 2/2.
5t ^ 2 – 30t + 25 = 0.
t2 – 6t + 5 = 0.
We calculate the time of movement by Vieta’s theorem: t1 = 1 s (the body will travel 25 m when lifting); t2 = 5 s (the body will travel 25 m when falling).
Answer: The body will be at a height of 25 m in 1 s.