Mechanical Aptitude Mechanical Aptitude Fluid Dynamics Principles 3 — Questions and Answers
Question 1: Oil with a specific gravity of 0.85 is resting on top of water. What does this tell you about the oil?
- Oil is denser than water and sinks
- Oil is less dense than water and floats (Correct answer)
- Oil and water have equal density
- Oil will mix completely with water
Correct answer: Oil is less dense than water and floats
Specific gravity less than 1.0 means the fluid is less dense than water, so oil floats on the water surface.
Question 2: A Venturi meter is used to measure:
- Fluid viscosity
- Fluid temperature
- Flow rate through a pipe (Correct answer)
- Fluid pressure at a static point
Correct answer: Flow rate through a pipe
A Venturi meter measures flow rate by detecting the pressure difference between a wide section and a narrow throat section of a pipe.
Question 3: At what point in a piping system is cavitation most likely to occur?
- Where pressure is highest
- Where fluid velocity is lowest
- Where pressure drops below the fluid's vapor pressure (Correct answer)
- At elbows in the pipe
Correct answer: Where pressure drops below the fluid's vapor pressure
Cavitation occurs when local pressure falls below the vapor pressure of the fluid, causing vapor bubbles to form.
Question 4: A tank has a hole near its base. As the water level in the tank drops, what happens to the velocity of water exiting the hole?
- Velocity increases
- Velocity decreases (Correct answer)
- Velocity stays constant
- Velocity first increases then decreases
Correct answer: Velocity decreases
By Torricelli's theorem, exit velocity = √(2gh), so as height h decreases, exit velocity decreases.
Question 5: In a hydraulic system, which of the following best describes Pascal's Law?
- Fluid flows from high pressure to low pressure only
- Pressure applied to a confined fluid is transmitted equally in all directions (Correct answer)
- Fluid velocity increases as pipe diameter decreases
- Buoyant force equals the weight of displaced fluid
Correct answer: Pressure applied to a confined fluid is transmitted equally in all directions
Pascal's Law states that pressure changes applied to an enclosed fluid are transmitted undiminished throughout the entire fluid.
Question 6: A pump rated at 2 HP is used to move water through a pipe. If friction losses consume 30% of the pump's power, how much power is actually delivered to the water?
- 0.6 HP
- 1.4 HP (Correct answer)
- 1.7 HP
- 2.3 HP
Correct answer: 1.4 HP
Power delivered to water = 2 HP × (1 − 0.30) = 2 × 0.70 = 1.4 HP.
Question 7: Which statement correctly describes the difference between gauge pressure and absolute pressure?
- Gauge pressure includes atmospheric pressure; absolute pressure does not
- Absolute pressure equals gauge pressure plus atmospheric pressure (Correct answer)
- They are always equal at sea level
- Gauge pressure is always greater than absolute pressure
Correct answer: Absolute pressure equals gauge pressure plus atmospheric pressure
Absolute pressure = gauge pressure + atmospheric pressure (approximately 14.7 psi at sea level).
Mechanical Aptitude Mechanical Aptitude Fluid Dynamics Principles 3
Oil with a specific gravity of 0.85 is resting on top of water.
What does this tell you about the oil?