A body weighing 800g, falling from a height of 3m, had a speed of 4m / s near the ground.

A body weighing 800g, falling from a height of 3m, had a speed of 4m / s near the ground. The work of the forces of resistance to the fall is equal to?

Initial data: m (body weight) = 800 g = 0.8 kg; H (body fall height) = 3 m; V (body speed at the ground) = 4 m / s; the fall is considered free (V0 = 0 m / s).
Reference data: g (acceleration due to gravity) = 10 m / s ^ 2.
We calculate the work of the resistance forces from the ratio:
Ac = E2 – E1 = Ek2 – (Ek1 + En2) = Ek2 – En2 = m * V ^ 2/2 – m * g * h = m * (V ^ 2/2 – g * h).
Let’s do the calculation:
Ac = 0.8 * (4 ^ 2/2 – 10 * 3) = -17.6 J.
Answer: The work of the forces of resistance to fall is 17.6 J.