FLUID MECHANICS FUNDAMENTALS
AND APPLICATIONS
(COMPREHENSIVE EXAM) QUESTIONS
AND ANSWERS
1. The continuum hypothesis is considered valid when the Knudsen number (Kn), the ratio of
the mean free path to the characteristic length, is:
A. Between 0.1 and 1
B. Less than 0.01
C. Greater than 10
D. Exactly 1
Answer: B
Conceptual Explanation: The continuum hypothesis holds when the mean free path of
molecules is much smaller than the characteristic length scale, typically Kn < 0.01.
2. How does the dynamic viscosity of a typical liquid behave with increasing temperature?
A. It increases exponentially
B. It increases linearly
C. It remains constant
,D. It decreases
Answer: D
Conceptual Explanation: In liquids, viscosity is dominated by intermolecular cohesive
forces, which weaken as temperature increases, leading to a decrease in viscosity.
3. The speed of sound in an ideal gas is proportional to:
A. The square of the absolute temperature
B. The inverse of the absolute temperature
C. The pressure only
D. The square root of the absolute temperature
Answer: D
Conceptual Explanation: The speed of sound in an ideal gas is given by c = sqrt(kRT),
where k is the specific heat ratio, R is the gas constant, and T is the absolute temperature.
4. For a submerged plane surface, the center of pressure is always:
A. Above the centroid of the surface
B. At the same level as the centroid
C. Below the centroid of the surface
D. At the water surface
Answer: C
, Conceptual Explanation: Because hydrostatic pressure increases with depth, the resultant
force acts at a point (center of pressure) lower than the geometric center (centroid).
5. A floating body is stable if:
A. The metacentric height (GM) is negative
B. The center of gravity is above the metacenter
C. The center of buoyancy is above the center of gravity
D. The metacentric height (GM) is positive
Answer: D
Conceptual Explanation: Stability for a floating body requires the metacenter (M) to be
above the center of gravity (G), meaning GM > 0.
6. The material derivative (D/Dt) represents:
A. Only the local rate of change with respect to time
B. The change in pressure along a streamline
C. Only the spatial rate of change
D. The total rate of change following a fluid particle
Answer: D
Conceptual Explanation: The material (or substantial) derivative includes both the local
acceleration (time) and convective acceleration (spatial) components.
AND APPLICATIONS
(COMPREHENSIVE EXAM) QUESTIONS
AND ANSWERS
1. The continuum hypothesis is considered valid when the Knudsen number (Kn), the ratio of
the mean free path to the characteristic length, is:
A. Between 0.1 and 1
B. Less than 0.01
C. Greater than 10
D. Exactly 1
Answer: B
Conceptual Explanation: The continuum hypothesis holds when the mean free path of
molecules is much smaller than the characteristic length scale, typically Kn < 0.01.
2. How does the dynamic viscosity of a typical liquid behave with increasing temperature?
A. It increases exponentially
B. It increases linearly
C. It remains constant
,D. It decreases
Answer: D
Conceptual Explanation: In liquids, viscosity is dominated by intermolecular cohesive
forces, which weaken as temperature increases, leading to a decrease in viscosity.
3. The speed of sound in an ideal gas is proportional to:
A. The square of the absolute temperature
B. The inverse of the absolute temperature
C. The pressure only
D. The square root of the absolute temperature
Answer: D
Conceptual Explanation: The speed of sound in an ideal gas is given by c = sqrt(kRT),
where k is the specific heat ratio, R is the gas constant, and T is the absolute temperature.
4. For a submerged plane surface, the center of pressure is always:
A. Above the centroid of the surface
B. At the same level as the centroid
C. Below the centroid of the surface
D. At the water surface
Answer: C
, Conceptual Explanation: Because hydrostatic pressure increases with depth, the resultant
force acts at a point (center of pressure) lower than the geometric center (centroid).
5. A floating body is stable if:
A. The metacentric height (GM) is negative
B. The center of gravity is above the metacenter
C. The center of buoyancy is above the center of gravity
D. The metacentric height (GM) is positive
Answer: D
Conceptual Explanation: Stability for a floating body requires the metacenter (M) to be
above the center of gravity (G), meaning GM > 0.
6. The material derivative (D/Dt) represents:
A. Only the local rate of change with respect to time
B. The change in pressure along a streamline
C. Only the spatial rate of change
D. The total rate of change following a fluid particle
Answer: D
Conceptual Explanation: The material (or substantial) derivative includes both the local
acceleration (time) and convective acceleration (spatial) components.
