How fast should a stone be thrown upwards so that its maximum lifting height is 15m?

According to the law of conservation of energy:
Eк1 + Eп1 = Eк2 + Eп2, where Eк1 and Eп1 are the energy during the throw; Eк2 and Ep2 – energy at max. height.
At max. height: V = 0, Eк2 = 0.
At the beginning of the throw: h = 0 m, Ep1 = 0 m.
Eк1 = Ep2.
Eк1 = (m * V0²) / 2, m – body mass, V0 – initial body speed (m / s).
Ep2 = m * g * h, g – gravitational acceleration (g = 10 m / s²), h – max. height (h = 15 m).
V0 = sqrt (2 * m * g * h) / m) = sqrt (2 * 10 * 15) = 17.32 m / s.
Answer: The initial velocity of the stone is 17.32 m / s.