A body without an initial speed falls from a height of H = 20m. Determine the speed of the body

A body without an initial speed falls from a height of H = 20m. Determine the speed of the body at a height of h = 15m. Disregard movement resistance.

According to the law of conservation of energy:
Eк1 + Eп1 = Eк2 + Eп2, where Eк1 and Eп1 – energy at a height of 20 m; Eк2 and Ep2 – energy at a height of 15 m.
Since at the beginning of the fall V = 0, then Eк1 = 0. Then
Ep1 = Ep2 + Eк2. Eк2 = Ep1 – Ep2.
Eк = (m * V ^ 2) / 2.
Ep = m * g * h, for Ep1 h = 20 m, for Ep1 h = 15 m. Therefore: Ep1 – Ep2 = 20 * m * g – 15 * m * g = 5 * m * g. We take g equal to 10 m / s ^ 2.
Hence: (m * V ^ 2) / 2 = 5 * m * g; V ^ 2 = 10 * g; V = sqrt (10 * 10) = sqrt100 = 10 m / s.
Answer. The speed of the body at a height of 15 m is 10 m / s.