Hydrostatic pressure derivation omits energy concepts

Steps:

• Consider a fluid column with cross-sectional area A and height h; volume V = A h.
• Mass of fluid m = density ρ × V = ρ A h.
• Weight (force) F = m × g = ρ A h g, where g is acceleration due to gravity.
• Pressure difference ΔP = F / A = ρ g h.

Why B is correct:

• The derivation relies on force balance from weight, not gravitational potential energy (mgh), which is an energy concept unrelated to direct pressure calculation.

Why the others are wrong:

• A: Density definition links mass to volume, essential for m = ρ A h.
• C: Pressure definition converts force to pressure via ΔP = F / A.
• D: Weight formula provides the downward force F = m g.

Final answer: B