OAR OAR Mechanical Comprehension: Fluids 3 — Questions and Answers
Question 1: A submarine descends from 100 ft to 200 ft below sea water. What happens to the pressure on its hull?
- Pressure doubles
- Pressure increases but does not double because surface pressure already exists (Correct answer)
- Pressure stays the same
- Pressure halves
Correct answer: Pressure increases but does not double because surface pressure already exists
Total pressure = atmospheric + hydrostatic; doubling depth doubles only the hydrostatic component, so total pressure increases but does not double.
Question 2: Which property of a fluid describes its resistance to flow?
- Density
- Viscosity (Correct answer)
- Surface tension
- Compressibility
Correct answer: Viscosity
Viscosity is the measure of a fluid's internal friction and resistance to deformation or flow.
Question 3: Water flows at 3 ft/s through a pipe with a 6 in² cross-section. What is the volumetric flow rate?
- 0.5 ft³/s
- 0.125 ft³/s (Correct answer)
- 18 ft³/s
- 2 ft³/s
Correct answer: 0.125 ft³/s
Q = A × v = (6/144 ft²) × 3 ft/s = 0.125 ft³/s (convert 6 in² to ft²).
Question 4: A sealed container is partially filled with water and then heated. What happens to the pressure inside?
- Pressure decreases because water expands
- Pressure increases because water vapor pressure rises (Correct answer)
- Pressure remains constant
- Pressure fluctuates randomly
Correct answer: Pressure increases because water vapor pressure rises
Heating increases vapor pressure and thermal expansion in a sealed container, raising internal pressure.
Question 5: Two connected tanks at the same elevation are filled with water. If Tank A has a larger cross-sectional area than Tank B, at equilibrium the water level in each tank is:
- Higher in the larger tank A
- Higher in the smaller tank B
- Equal in both tanks (Correct answer)
- Dependent on which tank was filled first
Correct answer: Equal in both tanks
Connected static fluids of the same type reach equal heights regardless of tank size (hydrostatic equilibrium).
Question 6: What does a manometer measure?
- Fluid velocity
- Fluid temperature
- Pressure difference between two points (Correct answer)
- Volumetric flow rate
Correct answer: Pressure difference between two points
A manometer uses a column of liquid to measure the pressure difference between two fluid regions.
Question 7: An object submerged in water weighs 10 lbs when measured underwater and 25 lbs when measured in air. What is the buoyant force?
- 10 lbs
- 15 lbs (Correct answer)
- 25 lbs
- 35 lbs
Correct answer: 15 lbs
Buoyant force = weight in air − weight in fluid = 25 − 10 = 15 lbs.
OAR OAR Mechanical Comprehension: Fluids 3
A submarine descends from 100 ft to 200 ft below sea water.
What happens to the pressure on its hull?