A depth of 5 m in fresh water (ρ ≈ 1000 kg/m^3) with atmospheric pressure P0 ≈ 101325 Pa is considered. What is the total pressure there?

A depth of 5 m in fresh water (ρ ≈ 1000 kg/m^3) with atmospheric pressure P0 ≈ 101325 Pa is considered. What is the total pressure there?

• A. About 101,325 Pa
• B. About 150,000 Pa
• C. About 200,000 Pa
• D. About 250,000 Pa

Answer: (B)

Pressure at depth comes from two parts: the atmospheric pressure at the surface and the pressure from the water column above you. The water part, called hydrostatic pressure, is ρ g h. With fresh water ρ ≈ 1000 kg/m^3, g ≈ 9.8 m/s^2, and h = 5 m, this is 1000 × 9.8 × 5 ≈ 49,000 Pa. Adding the surface pressure 101,325 Pa gives total pressure ≈ 150,325 Pa, about 1.5 × 10^5 Pa. So the depth experiences roughly 150,000 Pa of total pressure.

Pressure at depth comes from two parts: the atmospheric pressure at the surface and the pressure from the water column above you. The water part, called hydrostatic pressure, is ρ g h. With fresh water ρ ≈ 1000 kg/m^3, g ≈ 9.8 m/s^2, and h = 5 m, this is 1000 × 9.8 × 5 ≈ 49,000 Pa. Adding the surface pressure 101,325 Pa gives total pressure ≈ 150,325 Pa, about 1.5 × 10^5 Pa. So the depth experiences roughly 150,000 Pa of total pressure.