A body without an initial speed falls from a height of h = 20 m, determine the speed of the body at a height of h = 15 m.

These tasks: free fall; h0 (initial height) = 20 m; h (considered height) = 15 m.

Constants: by condition g (acceleration of gravity) = 10 N / kg.

1 way) Formula: h0 – h = Δh = S = V2 / 2a = V2 / 2g, whence we express: V = √ ((h0 – h) * 2 * g) = √ ((20 – 15) * 2 * 10 ) = 10 m / s.

Method 2) The law of conservation of energy: Ek1 + En1 = Ek0 and m * V1 ^ 2/2 + m * g * h = m * g * h0, whence we express: V1 ^ 2/2 = g * h0 – g * h and V1 = √ (2 * (g * h0 – g * h)) = √ (2 * (10 * 20 – 10 * 15)) = 10 m / s.

Answer: At a height of 15 m, the body will reach a speed of 10 m / s.