Ch-10: Mechanical Properties of Fluids30 Questions
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Try each question on your own first. Use Show Answer only after choosing an option. Then read the explanation and revisit the chapter notes if a concept is unclear.
Explanation: Hydrostatic pressure is the pressure exerted by a fluid at rest due to the weight of the fluid above a given point.
2. Pascal's law states that pressure applied to an enclosed fluid is
A. Transmitted undiminished to every point of the fluid and the walls of the container
B. Transmitted only in the direction of the applied force
C. Reduced as it travels through the fluid
D. Applicable only to gases
Answer: A. Transmitted undiminished to every point of the fluid and the walls of the container
Explanation: Pascal's law states that pressure applied anywhere to a confined incompressible fluid is transmitted equally in all directions throughout the fluid.
3. A hydraulic lift works on the principle of
A. Pascal's law
B. Archimedes' principle
C. Bernoulli's principle
D. Stokes' law
Answer: A. Pascal's law
Explanation: A hydraulic lift uses Pascal's law, where a small force applied to a small piston creates equal pressure that produces a much larger force on a bigger piston.
4. Atmospheric pressure at sea level is approximately
A. 1.013 × 10⁵ Pa
B. 1.013 × 10³ Pa
C. 1.013 × 10⁷ Pa
D. 1.013 Pa
Answer: A. 1.013 × 10⁵ Pa
Explanation: Standard atmospheric pressure at sea level is defined as 1.013 × 10⁵ Pa, equal to 1 atm or 760 mm of mercury.
5. Archimedes' principle states that the buoyant force on a body immersed in a fluid equals
A. The weight of the fluid displaced by the body
B. The weight of the body itself
C. The volume of the body
D. The pressure at the bottom of the fluid
Answer: A. The weight of the fluid displaced by the body
Explanation: Archimedes' principle states that the upward buoyant force on a submerged or floating body equals the weight of the fluid it displaces.
6. The equation of continuity for fluid flow is based on the conservation of
A. Mass
B. Energy
C. Momentum
D. Charge
Answer: A. Mass
Explanation: The equation of continuity (A₁v₁ = A₂v₂ for incompressible flow) follows from the conservation of mass in a flowing fluid.
7. Bernoulli's principle relates pressure, velocity, and
A. Height (elevation) of the fluid element
B. Temperature of the fluid
C. Viscosity of the fluid
D. Surface tension
Answer: A. Height (elevation) of the fluid element
Explanation: Bernoulli's equation states that the sum of pressure energy, kinetic energy, and potential energy per unit volume remains constant along a streamline for an ideal fluid.
8. According to Bernoulli's principle, where the speed of a fluid is high, the pressure is
A. Low
B. High
C. Unaffected
D. Equal to atmospheric pressure always
Answer: A. Low
Explanation: Bernoulli's principle implies that regions of high fluid speed correspond to regions of lower pressure, as seen in phenomena like aircraft lift.
9. The lift on an aircraft wing is explained using
A. Bernoulli's principle
B. Pascal's law
C. Archimedes' principle
D. Newton's law of viscosity
Answer: A. Bernoulli's principle
Explanation: The wing shape causes air to move faster over the top than the bottom, lowering pressure above and creating an upward lift force, explained by Bernoulli's principle.
10. The property of a fluid due to which it opposes relative motion between its layers is called
A. Viscosity
B. Surface tension
C. Buoyancy
D. Capillarity
Answer: A. Viscosity
Explanation: Viscosity is the internal frictional force that opposes relative motion between adjacent layers of a fluid.
11. The SI unit of coefficient of viscosity is
A. Pa·s (Poiseuille)
B. N/m
C. Pa
D. J/m²
Answer: A. Pa·s (Poiseuille)
Explanation: The SI unit of the coefficient of viscosity is pascal-second (Pa·s), also called the poiseuille (Pl).
12. Stokes' law gives the viscous drag force on a small sphere moving through a fluid as
A. F = 6πηrv
B. F = 4πηrv
C. F = πηr²v
D. F = 6πη²rv
Answer: A. F = 6πηrv
Explanation: Stokes' law states that the viscous drag force on a small spherical body moving through a viscous fluid is F = 6πηrv, where η is viscosity, r is radius, and v is velocity.
13. Terminal velocity of a body falling through a viscous fluid is reached when
A. The net force on the body becomes zero
B. The body stops accelerating and starts decelerating
C. The viscous force becomes zero
D. Gravity becomes zero
Answer: A. The net force on the body becomes zero
Explanation: Terminal velocity is reached when the viscous drag and buoyant force balance the weight of the body, so the net force and acceleration become zero.
14. Streamline flow of a fluid is also called
A. Laminar flow
B. Turbulent flow
C. Vortex flow
D. Compressible flow
Answer: A. Laminar flow
Explanation: In streamline or laminar flow, every particle passing a given point follows the same smooth path as particles before it, without mixing between layers.
15. Reynolds number is used to determine whether a fluid flow is
A. Laminar or turbulent
B. Compressible or incompressible
C. Viscous or non-viscous
D. Rotational or irrotational
Answer: A. Laminar or turbulent
Explanation: Reynolds number, a dimensionless quantity, predicts whether fluid flow will be laminar (low values) or turbulent (high values).
16. Surface tension of a liquid is defined as
A. Force per unit length acting along the surface
B. Force per unit area acting on the surface
C. Energy per unit volume of the liquid
D. Pressure difference across the surface
Answer: A. Force per unit length acting along the surface
Explanation: Surface tension is defined as the tangential force acting per unit length of an imaginary line drawn on the liquid surface.
17. Surface tension arises due to
A. Cohesive forces between liquid molecules
B. Gravitational force on liquid molecules
C. Adhesive forces with the container walls only
D. Viscous drag between layers
Answer: A. Cohesive forces between liquid molecules
Explanation: Surface tension arises because molecules at the liquid surface experience a net inward cohesive force, minimizing surface area.
18. A small insect can walk on water due to
A. Surface tension
B. Viscosity
C. Buoyancy alone
D. High density of water
Answer: A. Surface tension
Explanation: Surface tension creates a film-like layer at the water surface strong enough to support the weight of light insects like water striders.
19. The excess pressure inside a liquid drop of radius r and surface tension T is given by
A. 2T/r
B. 4T/r
C. T/r
D. T/2r
Answer: A. 2T/r
Explanation: For a spherical liquid drop with one surface, the excess pressure inside due to surface tension is given by 2T/r.
20. The excess pressure inside a soap bubble (having two surfaces) of radius r is
A. 4T/r
B. 2T/r
C. T/r
D. 8T/r
Answer: A. 4T/r
Explanation: A soap bubble has two surfaces (inner and outer), so the excess pressure inside is double that of a drop, given by 4T/r.
21. The rise or fall of a liquid in a narrow tube is called
A. Capillarity
B. Viscosity
C. Buoyancy
D. Diffusion
Answer: A. Capillarity
Explanation: Capillarity or capillary action is the rise or fall of liquid in a thin tube due to the interplay of surface tension, cohesion, and adhesion.
22. Water rises in a capillary tube while mercury falls, because
A. Water wets glass (adhesion dominant) while mercury does not (cohesion dominant)
B. Water is denser than mercury
C. Mercury has a lower surface tension than water
D. Water has zero viscosity
Answer: A. Water wets glass (adhesion dominant) while mercury does not (cohesion dominant)
Explanation: Water has a concave meniscus and rises since adhesive force with glass exceeds cohesive force, while mercury has strong cohesion and a convex meniscus, causing it to be depressed.
23. The angle of contact for a liquid that completely wets a solid surface is
A. Close to 0°
B. 90°
C. Close to 180°
D. Always 45°
Answer: A. Close to 0°
Explanation: A liquid that completely wets a surface, such as water on clean glass, has an angle of contact close to 0°.
24. As temperature increases, the surface tension of most liquids
A. Decreases
B. Increases
C. Remains constant
D. Becomes zero abruptly
Answer: A. Decreases
Explanation: As temperature rises, the intermolecular cohesive forces weaken, causing the surface tension of most liquids to decrease.
25. A ship made of steel floats on water mainly because
A. Its overall shape displaces enough water so buoyant force equals its weight
B. Steel is less dense than water
C. Surface tension of water supports it
D. Viscosity of water prevents it from sinking
Answer: A. Its overall shape displaces enough water so buoyant force equals its weight
Explanation: Although steel is denser than water, the hollow shape of a ship displaces a large volume of water, so the buoyant force balances the ship's weight, keeping it afloat.
26. A body floats in a liquid if its average density is
A. Less than or equal to the density of the liquid
B. Greater than the density of the liquid
C. Equal to zero
D. Independent of the liquid's density
Answer: A. Less than or equal to the density of the liquid
Explanation: A body floats when its average density is less than or equal to the density of the liquid, so the buoyant force can support its weight.
27. The variation of pressure with depth in a fluid at rest is given by
A. P = P₀ + ρgh
B. P = P₀ - ρgh
C. P = ρgh only
D. P = P₀ × ρgh
Answer: A. P = P₀ + ρgh
Explanation: The pressure at a depth h in a fluid of density ρ, with P₀ as pressure at the surface, is given by P = P₀ + ρgh.
28. A venturimeter is a device used to measure
A. The speed of flow of a fluid in a pipe
B. Viscosity of a fluid
C. Surface tension of a liquid
D. Density of a solid
Answer: A. The speed of flow of a fluid in a pipe
Explanation: A venturimeter uses Bernoulli's principle, measuring the pressure difference at a constriction in a pipe to determine the flow speed of the fluid.
29. Blood flow being faster through a narrowed (constricted) artery than a normal one is explained by the
A. Equation of continuity
B. Archimedes' principle
C. Pascal's law
D. Stokes' law
Answer: A. Equation of continuity
Explanation: By the equation of continuity, when the cross-sectional area of an artery decreases, the flow velocity must increase to keep the volume flow rate constant.
30. Detergents help clean clothes better than plain water mainly because they
A. Lower the surface tension of water, allowing it to penetrate fibers better
B. Increase the surface tension of water
C. Increase the viscosity of water
D. Have no effect on surface tension
Answer: A. Lower the surface tension of water, allowing it to penetrate fibers better
Explanation: Detergents act as surfactants that reduce the surface tension of water, helping it spread and penetrate into cloth fibers to remove dirt more effectively.
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