The boy, being on the balcony of the 3rd floor at a height of 10 m, throws a ball down at a speed of 4 m / s.

The boy, being on the balcony of the 3rd floor at a height of 10 m, throws a ball down at a speed of 4 m / s. How high the ball will bounce after the kick.

g = 9.8 m / s ^ 2.
V1 = 4 m / s.
h2 -?
Let us use the law of conservation of total mechanical energy: En1 + Ek1 = En2 + Ek2.
The potential energy of a body is determined by the formula: En1 = m * g * h1, En2 = m * g * h2.
The kinetic energy is determined by the formula: Ek1 = m * V1 ^ 2/2, Ek2 = m * V2 ^ 2/2.
Since the ball stopped at the top point, then V2 = 0 m / s, Ek2 = 0.
m * g * h1 + m * V1 ^ 2/2 = m * g * h2.
h2 = (m * g * h1 + m * V ^ 2/2) / m * g = (g * h1 + V ^ 2/2) / g.
h2 = (9.8 m / s ^ 2 * 10 m + (4 m / s) ^ 2/2) / 9.8 m / s ^ 2 = 10.8 m.
Answer: the ball will bounce to a height of h2 = 10.8 m.