A one-square inch column contains water to a height of 100 feet. What is the pressure in psi at the base of the column?

• A. 4.34
• B. .434
• C. 434
• D. 43.4

Answer: (D)

Pressure in a fluid increases with depth because the weight of the water above pushes down on the layer below. This relation, P = γ h (or P = ρ g h), links how high the column is to the pressure at the bottom. For water, the specific weight γ is about 62.4 lb_f per cubic foot, which converts to roughly 0.433 psi per foot. With a 100-foot column, the pressure at the base is 100 × 0.433 ≈ 43.3 psi, which rounds to 43.4 psi. The fact that the column is 1 square inch wide doesn’t change the pressure (pressure is the same regardless of area); it would only change the total force on the base, which would be about 43.4 pounds-force for that 1 in² area.