A concrete slab with a volume of 4 m3 is submerged in water. What force must be applied to keep it in the water.

To determine the magnitude of the holding force acting on the specified plate, we apply the formula: Fр = Fт – Fa = m * g – ρw * g * V = ρb * V * g – ρw * g * V = V * g * (ρb – ρw ).

Constants and variables: V – slab volume (V = 4 m3); g – acceleration due to gravity (g ≈ 10 m / s2); ρb is the density of the slab, concrete (density of heavy concrete ρb = 2000 … 2500 kg / m3; we take ρb = 2250 kg / m3); ρw is the density of the water in which the indicated plate is immersed (ρw = 1000 kg / m3);

Calculation: F = V * g * (ρb – ρv) = 4 * 10 * (2250 – 1000) = 50 * 10 ^ 3 N.

Answer: To hold the indicated plate in water, a force of 50 kN is required.