To what depth must one dive in the sea for the pressure to double relative to that at the surface?
A) Approximately 20 m
B) Approximately 10 m
C) Approximately 15 m
D) Approximately 2 m
E) Approximately 5 m
IMAT 2026 · Question 52
Q52 - Fluid mechanics
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The correct answer is B) Approximately 10 m.
At the surface the pressure is atmospheric, p₀ ≈ 1.0 × 10⁵ Pa. Under water, pressure grows with depth (Stevin’s law): p = p₀ + ρgh.
For the pressure to double, the water must add another p₀:
ρgh = p₀ → h = p₀ / (ρg) = 10⁵ / (1000 × 9.8) ≈ 10 m
A useful rule: every 10 m of water adds about 1 atmosphere. At 10 m the pressure is 2 atm; at 20 m it is 3 atm.
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