100 High-Scoring MCQs on Fluid Dynamics, Unit-6, Class 11 Physics (Unit-Wise Practice)

This post contains 100 carefully selected multiple-choice questions (MCQs) from Unit-6: Fluid Dynamics of Class 11 Physics, designed strictly according to the FBISE syllabus. These MCQs include a balanced mix of numerical and conceptual problems, making them exam-ready, revision-friendly, and high-scoring.

Whether you are preparing for annual board exams, chapter tests, or competitive entry tests, this collection thoroughly covers all the key concepts and formulas of Fluid Dynamics.

This unit-wise MCQ set includes questions from:

Ideal fluid and assumptions of fluid flow
Streamline flow and turbulent flow
Equation of continuity and applications
Bernoulli’s equation and its physical significance
Applications of Bernoulli’s principle (Venturi meter, lift of aerofoil, blood flow)
Torricelli’s theorem and speed of efflux
Viscous flow and coefficient of viscosity
Stokes’ law and terminal velocity
Drag force and motion of bodies in fluids
Real-life applications of fluid dynamics

Each MCQ is provided with the correct answer and a clear, concise explanation, helping students strengthen concepts, avoid common mistakes, and solve numericals confidently.

Prepare smartly, revise efficiently, and boost your exam score in Unit-6 Fluid Dynamics with these 100 high-yield MCQs.

MCQs No. 1

The unit of volume flow rate is:

a. m² s⁻¹
b. m³ s⁻¹
c. kg s⁻¹
d. m s⁻¹

The Correct Answer is option b. m³ s⁻¹

Explanation:
Volume flow rate is volume passing per unit time, so its unit is cubic meter per second.

MCQs No. 2

Which condition is necessary for the application of equation of continuity?

a. Compressible flow
b. Turbulent flow
c. Steady incompressible flow
d. Rotational flow

The Correct Answer is option c. Steady incompressible flow

Explanation:
The equation of continuity assumes constant density and steady flow.

MCQs No. 3

When the cross-sectional area of a pipe decreases, the velocity of an incompressible fluid:

a. Decreases
b. Remains same
c. Increases
d. Becomes zero

The Correct Answer is option c. Increases

Explanation:
According to continuity equation, $A v = \text{constant}$

MCQs No. 4

Which quantity remains constant in a steady incompressible flow?

a. Pressure
b. Velocity
c. Mass flow rate
d. Density gradient

The Correct Answer is option c. Mass flow rate

Explanation:
In steady incompressible flow, the same mass crosses all sections per second.

MCQs No. 5

Bernoulli’s equation is valid for a fluid which is:

a. Viscous
b. Compressible
c. Non-viscous and incompressible
d. Turbulent

The Correct Answer is option c. Non-viscous and incompressible

Explanation:
Energy loss due to viscosity is neglected in Bernoulli’s equation.

MCQs No. 6

If the speed of a fluid increases, its pressure:

a. Increases
b. Remains same
c. Decreases
d. Becomes zero

The Correct Answer is option c. Decreases

Explanation:
Bernoulli’s principle states that pressure and velocity are inversely related.

MCQs No. 7

Dynamic pressure of a fluid is given by:

a. ρv
b. ½ρv²
c. ρv²
d. v²

The Correct Answer is option b. ½ρv²

Explanation:
Dynamic pressure represents kinetic energy per unit volume.

MCQs No. 8

Terminal velocity of a body depends on:

a. Shape only
b. Mass only
c. Radius and viscosity of medium
d. Time of fall

The Correct Answer is option c. Radius and viscosity of medium

Explanation:
Terminal velocity is affected by viscous drag and size of the body.

MCQs No. 9

Drag force acting on a body at low speeds is proportional to:

a. Square of velocity
b. Velocity
c. Radius²
d. Area

The Correct Answer is option b. Velocity

Explanation:
At low speeds, viscous drag is directly proportional to velocity.

MCQs No. 10

Reynolds number is used to determine:

a. Pressure of fluid
b. Speed of fluid
c. Nature of flow
d. Density of fluid

The Correct Answer is option c. Nature of flow

Explanation:
Reynolds number predicts laminar or turbulent flow.

MCQs No. 11

Flow in which fluid particles move in parallel layers is called:

a. Turbulent flow
b. Chaotic flow
c. Laminar flow
d. Rotational flow

The Correct Answer is option c. Laminar flow

Explanation:
In laminar flow, layers slide smoothly without mixing.

MCQs No. 12

Critical velocity is the velocity at which flow changes from:

a. Turbulent to laminar
b. Laminar to turbulent
c. Steady to unsteady
d. Uniform to non-uniform

The Correct Answer is option b. Laminar to turbulent

Explanation:
Beyond critical velocity, flow becomes turbulent.

MCQs No. 13

Which factor does NOT affect viscosity of a liquid?

a. Temperature
b. Nature of liquid
c. Pressure (at ordinary conditions)
d. Intermolecular forces

The Correct Answer is option c. Pressure (at ordinary conditions)

Explanation:
Viscosity of liquids is mainly affected by temperature.

MCQs No. 14

Coefficient of viscosity has dimensions of:

a. ML⁻¹T⁻¹
b. ML⁻¹T⁻¹
c. MLT⁻²
d. L²T⁻¹

The Correct Answer is option b. ML⁻¹T⁻¹

Explanation:
From viscous force equation, viscosity has dimensions ML⁻¹T⁻¹.

MCQs No. 15

Venturi meter is used to measure:

a. Pressure
b. Density
c. Flow speed of fluid
d. Viscosity

The Correct Answer is option c. Flow speed of fluid

Explanation:
Venturi meter works on Bernoulli’s principle.

MCQs No. 16

Speed of efflux from a tank depends on:

a. Area of hole
b. Density of liquid
c. Depth of liquid above hole
d. Shape of tank

The Correct Answer is option c. Depth of liquid above hole

Explanation:
According to Torricelli’s theorem, speed depends on height.

MCQs No. 17

Lift on an aircraft wing is due to:

a. Gravity
b. Friction
c. Pressure difference
d. Weight of air

The Correct Answer is option c. Pressure difference

Explanation:
Higher air speed above wing creates lower pressure.

MCQs No. 18

In turbulent flow, the motion of fluid is:

a. Smooth
b. Regular
c. Irregular and chaotic
d. Parallel

The Correct Answer is option c. Irregular and chaotic

Explanation:
Turbulent flow is characterized by random fluctuations.

MCQs No. 19

The SI unit of pressure is:

a. Dyne
b. Bar
c. Pascal
d. Atmosphere

The Correct Answer is option c. Pascal

Explanation:
SI unit of pressure is newton per square meter, called pascal.

MCQs No. 20

When viscous force equals weight of a falling object, it moves with:

a. Zero velocity
b. Increasing velocity
c. Terminal velocity
d. Maximum acceleration

The Correct Answer is option c. Terminal velocity

Explanation:
At terminal velocity, net force becomes zero.

MCQs No. 21

Which condition is necessary for laminar flow?

a. High velocity
b. High density
c. Low velocity
d. High pressure

The Correct Answer is option c. Low velocity

Explanation:
Laminar flow occurs at low speeds where viscous forces dominate.

MCQs No. 22

The equation of continuity is valid only when the fluid is:

a. Compressible
b. Viscous
c. Incompressible
d. Turbulent

The Correct Answer is option c. Incompressible

Explanation:
Continuity equation assumes constant density of fluid.

MCQs No. 23

Bernoulli’s equation is simply ________.
a. law of conservation of mass
b. law of conservation of energy
c. law of continuity
d. none

The Correct Answer is option b. law of conservation of energy

Explanation:
It’s a statement of the law of conservation of energy that energy carried by fluid in motion remains conserved.

MCQs No. 24

Water flows through a pipe of area 0.02 m² with speed 3 m/s. What is the volume flow rate?

a. 0.02 m³/s
b. 0.04 m³/s
c. 0.06 m³/s
d. 0.6 m³/s

The Correct Answer is option c. 0.06 m³/s

Explanation:
Volume flow rate $Q = Av = 0.02 \times 3 = 0.06 \, \text{m}^3/\text{s}$

MCQs No. 25

Speed of water in a pipe is 4 m/s. If cross-sectional area becomes half, the new speed is:

a. 2 m/s
b. 4 m/s
c. 8 m/s
d. 16 m/s

The Correct Answer is option c. 8 m/s

Explanation:
Using continuity equation $A_1v_1 = A_2v_2$

MCQs No. 26

A liquid flows at 5 m/s through a pipe of area 0.01 m². The mass flow rate (ρ = 1000 kg/m³) is:

a. 5 kg/s
b. 10 kg/s
c. 50 kg/s
d. 500 kg/s

The Correct Answer is option c. 50 kg/s

Explanation:
Mass flow rate = ρAv = 1000 × 0.01 × 5 = 50 kg/s.

MCQs No. 27

Calculate dynamic pressure of air (ρ = 1.2 kg/m³) moving at 10 m/s.

a. 12 Pa
b. 60 Pa
c. 120 Pa
d. 600 Pa

The Correct Answer is option b. 60 Pa

Explanation:
Dynamic pressure = ½ρv² = ½ × 1.2 × 10² = 60 Pa.

MCQs No. 28

Water issues from a hole 5 m below the surface. Speed of efflux is (g = 9.8 m/s²):

a. 7 m/s
b. 9.9 m/s
c. 14 m/s
d. 49 m/s

The Correct Answer is option b. 9.9 m/s

Explanation:
$v = \sqrt{2gh} = \sqrt{2×9.8×5} ≈ 9.9 \, \text{m/s}$

MCQs No. 29

A drop falls with terminal velocity 2 m/s. If its radius is doubled, new terminal velocity is:

a. 1 m/s
b. 2 m/s
c. 4 m/s
d. 8 m/s

The Correct Answer is option c. 4 m/s

Explanation:
Terminal velocity ∝ r², so doubling radius makes velocity four times.

MCQs No. 30

Pressure difference between two points in a pipe is 2000 Pa. Density of liquid is 1000 kg/m³. Velocity difference is:

a. 1 m/s
b. 2 m/s
c. 3 m/s
d. 4 m/s

The Correct Answer is option b. 2 m/s

Explanation:
Using Bernoulli’s equation: ΔP = ½ρ(v₂² − v₁²).

MCQs No. 31

What do we call the maximum velocity of a fluid in a tube for which the flow remains streamlined?

a. Hyper velocity
b. Critical velocity
c. Stream velocity
d. Laminar velocity

The Correct Answer is option b. Critical velocity

Explanation:
Critical velocity is the maximum speed up to which fluid flow remains laminar. Beyond this speed, the flow becomes turbulent.

MCQs No. 32

A venturi meter measures the flow of water in a pipe of area 0.0038 m² and throat area 0.00031 m². If the pressure difference is 2.4 kPa, what is the speed of water in the pipe?

a. 2.1 m/s
b. 2.2 m/s
c. 2.3 m/s
d. 2.4 m/s

The Correct Answer is option b. 2.2 m/s

Explanation:
The venturi meter works on Bernoulli’s principle and the equation of continuity to calculate fluid speed.

MCQs No. 33

Density of water is ______.

a. 900 kg m⁻³
b. 950 kg m⁻³
c. 1000 kg m⁻³
d. 1050 kg m⁻³

The Correct Answer is option c. 1000 kg m⁻³

Explanation:
Density is mass per unit volume. One cubic meter of water has a mass of 1000 kg.

MCQs No. 34

What happens to the viscosity of a liquid with increase in temperature?

a. It increases
b. It decreases
c. Remains constant
d. No change

The Correct Answer is option b. It decreases

Explanation:
As temperature increases, molecular motion increases, reducing internal resistance and hence viscosity decreases.

MCQs No. 35

Viscosity means opposition offered by different layers of flowing fluid by:

a. Itself
b. Other liquid
c. Water
d. Alcohol

The Correct Answer is option a. Itself

Explanation:
Viscosity is the internal resistance offered by one layer of a fluid to the motion of another layer of the same fluid.

MCQs No. 36

The rate of change of viscosity with temperature is measured by an arbitrary scale called:

a. Arbitrary constant
b. Viscosity constant
c. Viscosity index
d. Arbitrary index

The Correct Answer is option c. Viscosity index

Explanation:
Viscosity index indicates how much the viscosity of a lubricant changes with temperature.

MCQs No. 37

Oil whose viscosity changes rapidly with temperature has:

a. High viscosity index
b. Low viscosity index
c. Moderate viscosity index
d. Zero viscosity index

The Correct Answer is option d. Zero viscosity index

Explanation:
If viscosity changes sharply with temperature, the viscosity index is very low or zero.

MCQs No. 38

The viscosity of lubricating oil must be ______ to keep it in position.

a. Greater than zero
b. Less than zero
c. Equal to zero
d. None

The Correct Answer is option a. Greater than zero

Explanation:
A lubricant must have sufficient viscosity to remain between surfaces and reduce friction.

MCQs No. 39

Frictional effect between layers of flowing fluid is known as:

a. Viscosity
b. Friction
c. Gravity
d. Surface tension

The Correct Answer is option a. Viscosity

Explanation:
Viscosity represents internal friction between fluid layers during flow.

MCQs No. 40

A body with large cross-section will have:

a. Lower drag
b. Higher drag force
c. Same drag
d. No drag

The Correct Answer is option b. Higher drag force

Explanation:
Drag force increases with the cross-sectional area of the body.

MCQs No. 41

Viscosity of water at high temperature compared to low temperature is:

a. More
b. Same
c. Less
d. Infinite

The Correct Answer is option c. Less

Explanation:
Viscosity of liquids decreases with temperature.

MCQs No. 42

The SI unit of volume flow rate is:

a. m²/s
b. kg/s
c. m³/s
d. m/s

The Correct Answer is option c. m³/s

Explanation:
Volume per unit time is measured in cubic meters per second.

MCQs No. 43

Water flows through a 4 cm radius pipe at 2 m/s. Flow rate is:

a. 0.025 m³/s
b. 0.010 m³/s
c. 0.50 m³/s
d. 1.0 m³/s

The Correct Answer is option b. 0.010 m³/s

Explanation:
A = πr² = π(0.04)² ≈ 0.005 m²
Q = Av = 0.005 × 2 = 0.01 m³/s.

MCQs No. 44

If velocity of fluid becomes zero, pressure energy becomes:

a. Zero
b. Maximum
c. Maximum
d. Minimum

The Correct Answer is option c. Maximum

Explanation:
According to Bernoulli’s equation, when velocity decreases, pressure increases.

MCQs No. 45

The drag coefficient has value:

a. With unit
b. Without unit
c. In meters
d. In seconds

The Correct Answer is option b. Without unit

Explanation:
Drag coefficient is a dimensionless quantity.

MCQs No. 46

Speed of water in a pipe is 6 m/s. If area is tripled, new speed is:

a. 18 m/s
b. 6 m/s
c. 2 m/s
d. 3 m/s

The Correct Answer is option c. 2 m/s

Explanation:
Using continuity equation: $v \propto 1/ A$ .

MCQs No. 47

At terminal velocity, acceleration of body is:

a. Maximum
b. Minimum
c. Zero
d. Infinite

The Correct Answer is option c. Zero

Explanation:
Net force becomes zero at terminal velocity.

MCQs No. 48

A liquid flows steadily. Which quantity remains constant?

a. Pressure
b. Velocity
c. Mass flow rate
d. Area

The Correct Answer is option c. Mass flow rate

Explanation:
Mass is conserved in steady incompressible flow.

MCQs No. 49

If density of liquid is doubled, dynamic pressure becomes:

a. Half
b. Same
c. Double
d. Four times

The Correct Answer is option c. Double

Explanation:
Dynamic pressure = ½ρv² ∝ density.

MCQs No. 50

A pipe has diameter reduced to half. The speed of fluid becomes:

a. Same
b. Double
c. Four times
d. Half

The Correct Answer is option c. Four times

Explanation:

Area ∝ diameter², so reducing diameter to half reduces area to one-fourth, increasing speed four times.

MCQs No. 51

What is the dimension of drag coefficient?

a. N/s
b. m/s
c. kg/s
d. Dimensionless

The Correct Answer is option d. Dimensionless

Explanation:
Drag coefficient has no dimensions and depends only on shape and flow conditions.

MCQs No. 52

Drag force between two layers of liquid is:

a. Non-zero
b. Zero
c. Infinite
d. None

The Correct Answer is option a. Non-zero

Explanation:
Adjacent layers of liquid exert viscous drag on each other.

MCQs No. 53

When drag force equals the weight of a falling drop, the net force becomes:

a. 1
b. Zero
c. Maximum
d. Minimum

The Correct Answer is option b. Zero

Explanation:
When net force is zero, acceleration becomes zero and the object moves with terminal velocity.

MCQs No. 54

At very high speed, drag force is proportional to the:

a. Speed of fluid
b. Square of speed of object
c. Square of radius
d. Radius

The Correct Answer is option b. Square of speed of object

Explanation:
At high speeds, drag force varies as the square of velocity.

MCQs No. 55

______ flow occurs at high velocity and low viscosity.

a. Chaotic
b. Turbulent
c. Laminar
d. Ideal

The Correct Answer is option b. Turbulent

Explanation:
High velocity and low viscosity favor turbulent flow.

MCQs No. 56

If every particle follows the same path, the flow is:

a. Laminar
b. Turbulent
c. Chaotic
d. Steady chaotic

The Correct Answer is option a. Laminar

Explanation:
In laminar flow, fluid layers move smoothly without mixing.

MCQs No. 57

Reynolds number gives the relative importance of:

a. Viscous and pressure force
b. Inertial force and viscous force
c. Pressure and inertia
d. Momentum and pressure

The Correct Answer is option b. Inertial force and viscous force

Explanation:
Reynolds number predicts whether flow is laminar or turbulent.

MCQs No. 58

According to equation of continuity, when speed increases, area:

a. Increases
b. Decreases
c. Remains same
d. Changes randomly

The Correct Answer is option b. Decreases

Explanation:
For incompressible flow, $A v = constant$ .

MCQs No. 59

The equation of continuity is based on:

a. Conservation of mass
b. Conservation of momentum
c. Conservation of energy
d. Conservation of force

The Correct Answer is option a. Conservation of mass

Explanation:
Mass flow rate remains constant in steady incompressible flow.

MCQs No. 60

Bernoulli’s equation is based on conservation of:

a. Energy
b. Mass
c. Momentum
d. None

The Correct Answer is option a. Energy

Explanation:
Bernoulli’s equation is a statement of conservation of mechanical energy in fluid flow.

MCQs No. 61

If fluid is incompressible and steady, its mass is:

a. Increase
b. Decreased
c. Either increase or decrease
d. Conserved

The Correct Answer is option d. Conserved

Explanation:
For incompressible and steady flow, mass entering a section equals mass leaving it.

MCQs No. 62

The constant in the equation of continuity is known as:

a. Flow rate
b. Fluid flow
c. Friction
d. Surface tension

The Correct Answer is option a. Flow rate

Explanation:
In continuity equation $A v = constant$ , this constant represents volume flow rate.

MCQs No. 63

For an incompressible flow, mass continuity becomes:

a. Energy equation
b. Momentum equation
c. Volume continuity equation
d. Remains same

The Correct Answer is option c. Volume continuity equation

Explanation:
Since density is constant, mass conservation reduces to volume conservation.

MCQs No. 64

The quantity specifying the flow or motion is called:

a. Density
b. Flux
c. Field
d. Electrostatic force

The Correct Answer is option b. Flux

Explanation:
Flux represents the rate at which a quantity flows through a surface.

MCQs No. 65

Which of the following is an incompressible flow?

a. Gas
b. Sponge
c. Water
d. Gel

The Correct Answer is option c. Water

Explanation:
Liquids like water have nearly constant density, so they are incompressible.

MCQs No. 66

Mass can neither be created nor destroyed is the principle of:

a. Energy equation
b. Momentum equation
c. Continuity equation
d. None

The Correct Answer is option c. Continuity equation

Explanation:
The continuity equation is based on conservation of mass.

MCQs No. 67

If a system is in steady state, it is in:

a. Equilibrium state only
b. Steady state only
c. Both A & B
d. None

The Correct Answer is option b. Steady state only

Explanation:
Steady state means properties do not change with time, but equilibrium is not necessary.

MCQs No. 68

According to Bernoulli’s equation, pressure of fast moving fluid is:

a. Directly related to speed
b. Directly related to area
c. Inversely related to speed
d. None

The Correct Answer is option c. Inversely related to speed

Explanation:
As velocity increases, pressure decreases.

MCQs No. 69

Relation between pressure and velocity in non-viscous incompressible flow is:

a. P = constant
b. P + ½ρv² = constant
c. ½ρv² = 0
d. P + ½ρv² = 0

The Correct Answer is option b. P + ½ρv² = constant

Explanation:
This is Bernoulli’s equation for horizontal flow.

MCQs No. 70

Bernoulli’s equation is applicable for:

a. Irrotational flow
b. Viscous flow
c. Incompressible flow
d. Compressible flow

The Correct Answer is option c. Incompressible flow

Explanation:
Bernoulli’s equation assumes constant density and no viscosity.

MCQs No. 71

Bernoulli’s equation cannot be applied directly to:

a. Ideal flow
b. Viscous flow
c. Both A & B
d. None

The Correct Answer is option b. Viscous flow

Explanation:
Energy is lost due to viscosity, so Bernoulli’s equation fails.

MCQs No. 72

Aircraft fly based on:

a. Newton’s third law
b. Conservation of mass
c. Bernoulli’s principle
d. Gravity

The Correct Answer is option c. Bernoulli’s principle

Explanation:
Higher air speed above wings causes lower pressure, producing lift.

MCQs No. 73

Dynamic pressure is given by:

a. ½ρv²
b. ρv²
c. 3v²
d. 5ρv²

The Correct Answer is option a. ½ρv²

Explanation:
Dynamic pressure represents kinetic energy per unit volume of fluid.

MCQs No. 74

Speed of water emerging from a hole 10 m below surface is:

a. 10 m/s
b. 14 m/s
c. 195 m/s
d. 0.1 m/s

The Correct Answer is option b. 14 m/s

Explanation:
Using Torricelli’s theorem: $v = \sqrt{2gh}$

MCQs No. 75

According to Bernoulli’s equation, where speed is high, pressure is:

a. High
b. Low
c. Maximum
d. Minimum

The Correct Answer is option b. Low

Explanation:
Pressure and velocity are inversely related.

MCQs No. 76

Speed of efflux is determined by:

a. Bernoulli’s theorem
b. Torricelli’s theorem
c. Continuity equation
d. None

The Correct Answer is option b. Torricelli’s theorem

Explanation:
Torricelli’s theorem gives speed of liquid flowing out of a tank.

MCQs No. 77

Blood vessels are:

a. Rigid
b. Not rigid
c. Of glass
d. Of rubber

The Correct Answer is option b. Not rigid

Explanation:
Blood vessels are elastic and flexible.

MCQs No. 78

1 torr is equal to:

a. 1.333 Pa
b. 13.33 Pa
c. 133.33 Pa
d. 1333.3 Pa

The Correct Answer is option c. 133.33 Pa

Explanation:
Standard conversion: 1 torr = 133.33 pascal.

MCQs No. 79

Aerofoil is perfectly:

a. Streamlined
b. Turbulent
c. Elastic
d. None

The Correct Answer is option a. Streamlined

Explanation:
Streamlined shape reduces drag and increases lift.

MCQs No. 80

Terminal velocity refers to:

a. Zero velocity
b. Increasing velocity
c. Decreasing velocity
d. Constant velocity

The Correct Answer is option d. Constant velocity

Explanation:
At terminal velocity, net force becomes zero.

MCQs No. 81

SI unit of coefficient of viscosity is:

a. Nm²
b. N s m⁻²
c. Nsm⁻¹
d. Ns⁻¹m⁻²

The Correct Answer is option b. N s m⁻²

Explanation:
Viscosity = force × time / area.

MCQs No. 82

The equation of continuity for fluid flow is derived from conservation of:

a. Volume
b. Mass
c. Energy
d. Pressure

The Correct Answer is option b. Mass

Explanation:
Continuity equation states that mass entering a system per unit time equals mass leaving it.

MCQs No. 83

Blood flows at a rate of 200 cm³/s through a capillary of cross-sectional area 0.5 m². The velocity in mm/s is:

a. 0.4
b. 0.3
c. 0.2
d. 0.1

The Correct Answer is option a. 0.4

Explanation:
Using continuity equation $AV = \text{constant}$ :
$V = 4 \times 10^{-4}\,\text{m/s} = 0.4\,\text{mm/s}$

MCQs No. 84

The pressure of a fluid is low where its speed is:

a. Zero
b. Low
c. Constant
d. High

The Correct Answer is option d. High

Explanation:
According to Bernoulli’s principle, higher speed results in lower pressure.

MCQs No. 85

With increase in temperature, viscosity of a fluid:

a. Increases
b. Decreases
c. Becomes double
d. Remains constant

The Correct Answer is option b. Decreases

Explanation:
Increase in temperature reduces intermolecular attraction, lowering viscosity.

MCQs No. 86

Terminal velocity of a falling body is:

a. Zero
b. Increasing
c. Decreasing
d. Constant

The Correct Answer is option d. Constant

Explanation:
At terminal velocity, drag force equals weight and acceleration becomes zero.

MCQs No. 87

Bernoulli’s equation is based on conservation of:

a. Mass
b. Momentum
c. Energy
d. Force

The Correct Answer is option c. Energy

Explanation:
Bernoulli’s equation expresses conservation of mechanical energy in fluid flow.

MCQs No. 88

A rain drop of radius r falls with terminal velocity $V_1$ . The terminal velocity of a drop of radius 2r is:

a. $V_1/2$
b. $2V_1$
c. $4V_1$
d. None

The Correct Answer is option b. $2V_1$

Explanation:
Terminal velocity is proportional to the square of radius, so doubling radius doubles velocity.

MCQs No. 89

Pressure is inversely related to velocity according to:

a. Newton’s law
b. Continuity equation
c. Bernoulli’s principle
d. Pascal’s law

The Correct Answer is option c. Bernoulli’s principle

Explanation:
Bernoulli’s principle states that pressure decreases as velocity increases.

MCQs No. 90

Capillaries are the:

a. Largest blood vessels
b. Smallest blood vessels
c. Veins
d. None

The Correct Answer is option b. Smallest blood vessels

Explanation:
Capillaries are extremely thin vessels where exchange of materials occurs.

MCQs No. 91

When the radius of an artery decreases, the blood pressure:

a. Increased
b. Decreased
c. Remains same
d. Becomes zero

The Correct Answer is option b. Decreased

Explanation:
As flow speed increases in narrow arteries, pressure decreases (Bernoulli’s principle).

MCQs No. 92

Aerofoil lift depends mainly on:

a. Weight of aircraft
b. Shape of wings
c. Pressure difference
d. Density of metal

The Correct Answer is option c. Pressure difference

Explanation:
Lift is produced due to pressure difference between upper and lower wing surfaces.

MCQs No. 93

The SI unit of coefficient of viscosity is:

a. Nm²
b. N·s·m⁻²
c. N·s·m⁻¹
d. N·m⁻²

The Correct Answer is option b. N·s·m⁻²

Explanation:
Coefficient of viscosity represents resistance to flow per unit area per velocity gradient.

MCQs No. 94

A body experiences drag force proportional to velocity. The flow is:
a. Turbulent
b. Chaotic
c. Laminar
d. Rotational
The Correct Answer is option c. Laminar
Explanation:
In laminar flow, drag ∝ velocity.

MCQs No. 95

Reynolds number of a flow is 1500. The flow is:
a. Turbulent
b. Chaotic
c. Laminar
d. Unsteady
The Correct Answer is option c. Laminar
Explanation:
Flow is laminar when Reynolds number < 2000.

MCQs No. 96

If Reynolds number becomes very large, the flow is:
a. Laminar
b. Turbulent
c. Steady
d. Ideal
The Correct Answer is option b. Turbulent

Explanation:
Large Reynolds number indicates dominance of inertial forces.

MCQs No. 97

Water flows through a horizontal pipe. At one point, the pressure is $2.5 \times 10^{5}\,\text{Pa}$ and speed is 3 m/s. If the speed at another point is 5 m/s, find the pressure there. (Density of water = 1000 kg/m³)

a. $2.46 \times 10^{5}\,\text{Pa}$
b. $2.42 \times 10^{5}\,\text{Pa}$
c. $2.50 \times 10^{5}\,\text{Pa}$
d. $2.38 \times 10^{5}\,\text{Pa}$

The Correct Answer is option b. $2.42 \times 10^{5}\,\text{Pa}$

Explanation:
Using Bernoulli’s equation:
$P_1 + \frac{1}{2}\rho v_1^2 = P_2 + \frac{1}{2}\rho v_2^2$

MCQs No. 98

Water flows through a pipe of radius 4 cm with speed 2 m/s. If the radius becomes 2 cm, the new speed is:

a. 4 m/s
b. 8 m/s
c. 16 m/s
d. 2 m/s

The Correct Answer is option b. 8 m/s

Explanation:
Area ∝ r².
When radius is halved, area becomes one-fourth, so speed becomes four times.

MCQs No. 99

A liquid emerges from a small hole at a depth of 1.25 m below the surface. What is the speed of efflux? (g = 10 m/s²)

a. 3 m/s
b. 5 m/s
c. 7 m/s
d. 10 m/s

The Correct Answer is option b. 5 m/s

Explanation:
Using Torricelli’s theorem:
$v = \sqrt{2gh} = \sqrt{2×10×1.25} = 5 \,\text{m/s}$

MCQs No. 100

A steel ball of radius r falls through a viscous liquid with terminal velocity 4 m/s. If the radius becomes 3r, the new terminal velocity is:

a. 12 m/s
b. 36 m/s
c. 6 m/s
d. 9 m/s

The Correct Answer is option b. 36 m/s

Explanation:
Terminal velocity ∝ r²
$(3r)^2 = 9r^2$
So new velocity = $9 × 4 = 36$ m/s.

100 High-Scoring MCQs on Fluid Dynamics | Class 11 Physics | Unit 6