TFS · Hydraulic & Fluid Applications · Problem 29PDFSolution in PDF ↓
TFS · Hydraulic & Fluid Applications · Problem 29
Problem & Solution
Video Synthesis
Topic: Hydraulic & Fluids Applications — What is the stagnation pressure at the nose of a submarine traveling 20 miles per hour horizontally at a depth of 200 feet?
Method: Assume the ocean is stationary and the specific gravity of water can be taken as one.
Key values: 62.4 pound force per cubic feet, 86.58 PSI, 200 feet
Reference: reference handbook
✅ Answer: D
Office Hours
2
Student questions asked in live office hours about this problem
OH 88
Q: Why didn't we include atmospheric pressure in the stagnation pressure calculation for the submarine nose?
A: Stagnation pressure is the same as Pitot tube pressure, which measures the total of static pressure plus dynamic pressure from velocity. The static pressure at depth already accounts for all pressure effects at that location, so we don't add atmospheric pressure separately—it's already embedded in the hydrostatic pressure calculation.
OH 117 · March 30, 2026
Q: The student asks whether atmospheric pressure should be added to the hydrostatic pressure term in the stagnation pressure equation for a submarine at 200 feet depth, noting they were confused after overcorrecting from a previous problem where they had incorrectly omitted atmospheric pressure.
A: Dan confirms the student is correct — atmospheric pressure should be included in the static pressure term, as the total static pressure on a submarine at 200 feet is the sum of the water column pressure plus the atmospheric pressure acting on the ocean surface (equivalent to ~34 feet of water head). Omitting atmospheric pressure at 200 feet depth introduces roughly a 16-17% error in the static pressure term, which is too significant to neglect. Dan notes this is only ignorable at very great depths where atmospheric pressure becomes negligible relative to the hydrostatic pressure.