Absolute pressure at depth
A diver is 20 m below the surface of fresh water (ρ = 1000 kg/m³, g = 10 m/s², Patm ≈ 1 × 10⁵ Pa). What is the absolute pressure on the diver?
Answer C: explanation for every choice
A
This is atmospheric pressure alone.
B
This is the gauge pressure, ρgh, without atmospheric pressure.
C
Correct. P = Patm + ρgh = 1 × 10⁵ + (1000)(10)(20) = 3 × 10⁵ Pa.
D
This is off by a factor of 10 in the ρgh term.
TakeawayAbsolute pressure = Patm + ρgh. Each 10 m of water adds about 1 atm.
Equation usedHydrostatic pressure
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