Mechanical Aptitude Mechanical Aptitude Fluid Dynamics Principles 5 — Questions and Answers
Question 1: An airplane wing generates lift primarily because:
- The wing is heavier on top than on the bottom
- Air moves faster over the curved top surface, reducing pressure there (Correct answer)
- Air pressure is always greater above a wing
- The flat bottom surface reflects air downward without a pressure change
Correct answer: Air moves faster over the curved top surface, reducing pressure there
The wing's curved upper surface causes air to speed up, which by Bernoulli's principle reduces pressure on top relative to the bottom, generating lift.
Question 2: In a pipe system, what is the purpose of a check valve?
- To regulate flow rate
- To prevent backflow of fluid (Correct answer)
- To measure pressure drop
- To filter contaminants from the fluid
Correct answer: To prevent backflow of fluid
A check valve is a one-way valve that allows fluid to flow in only one direction, automatically closing if flow tries to reverse.
Question 3: A fluid flowing through a pipe that makes a 90° bend will experience which of the following?
- A reduction in pipe friction
- Additional pressure loss due to the change in flow direction (Correct answer)
- An increase in flow velocity at the bend
- No change compared to a straight pipe
Correct answer: Additional pressure loss due to the change in flow direction
Bends, elbows, and fittings create additional losses called minor losses due to turbulence and flow separation at the direction change.
Question 4: What is the definition of 'flow rate' in a fluid system?
- The speed at which fluid particles move
- The volume of fluid passing a point per unit of time (Correct answer)
- The pressure difference between two pipe sections
- The force exerted by the fluid on the pipe walls
Correct answer: The volume of fluid passing a point per unit of time
Flow rate (volumetric) is the volume of fluid that passes through a cross-section per unit time, commonly expressed in gallons per minute (GPM) or liters per second.
Question 5: Which of the following describes the function of a pressure relief valve in a hydraulic circuit?
- It boosts system pressure when demand increases
- It limits maximum system pressure to protect components (Correct answer)
- It converts flow rate into pressure
- It removes air bubbles from the hydraulic fluid
Correct answer: It limits maximum system pressure to protect components
A pressure relief valve opens automatically when system pressure exceeds a set limit, diverting fluid back to the reservoir to protect pumps and components.
Question 6: Compared to water, a very viscous oil flowing through the same pipe at the same velocity is more likely to exhibit:
- Turbulent flow
- Laminar flow (Correct answer)
- Cavitation
- Water hammer
Correct answer: Laminar flow
Higher viscosity increases resistance to turbulence; at the same velocity, viscous oils have lower Reynolds numbers and are more likely to flow laminarly.
Question 7: A hydraulic cylinder with a bore of 3 inches is supplied with oil at 1,000 psi. Approximately what force does the cylinder produce?
- 942 lb
- 3,000 lb
- 7,069 lb (Correct answer)
- 9,425 lb
Correct answer: 7,069 lb
Force = Pressure × Area = 1,000 psi × π×(1.5)² ≈ 1,000 × 7.07 ≈ 7,069 lb.
Mechanical Aptitude Mechanical Aptitude Fluid Dynamics Principles 5
An airplane wing generates lift primarily because: