Fluid Dynamics MCQs – 100 Advanced & Numerical MCQs with Solutions | ECAT, MDCAT & Engineering Entry Tests

100 Advanced & Numerical MCQs (Level -2) on Fluid Dynamics, Physics (Unit-Wise MCQs Practice):

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👉Physics MCQs Hub – Unit wise Physics MCQs Practice (Main-Page)👈

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Whether you are preparing for Board Exams, school tests, college assessments, university exams, ECAT, MDCAT, NTS, PIEAS, GIKI, UET, FAST, NUST, or other competitive examinations, this comprehensive Fluid Dynamics MCQs Collection is designed to strengthen your conceptual understanding and problem-solving skills.

This chapter covers all the essential topics, including ideal and real fluids, streamline and turbulent flow, equation of continuity, Bernoulli's principle, pressure in moving fluids, viscosity, coefficient of viscosity, Stokes' law, Reynolds number, drag force, terminal velocity, critical velocity, Torricelli's theorem, Venturi meter, Pitot tube, atomizer, carburetor, filter pump, lift on aircraft wings, aerodynamic design, and real-life applications of fluid mechanics.

The MCQs are organized into four progressive sections:

100 Basic MCQs Level -1 (1 - 100) – Build a strong foundation with essential concepts, definitions, principles, laws, and formulas.

100 Advanced & Numerical MCQs (101 -200) – Strengthen your calculation, analytical thinking, and application-based problem-solving skills through challenging numerical and conceptual questions.

50 Higher-Order Thinking Skills (HOTS) MCQs 201 - 250) – Challenge yourself with conceptual reasoning, real-life applications, assertion-reason questions, engineering scenarios, and competitive exam-level problems.

50 Challenging MCQs Quiz with Answers – A carefully selected mix of conceptual, numerical, and HOTS questions designed for quick revision, self-assessment, and complete exam preparation.

Every MCQ Includes:

✔ Four carefully designed answer options

✔ Instant correct answer

✔ Detailed concept-based explanation

✔ Exam-focused learning approach

This collection is ideal for Board Exams, FBISE, ECAT, MDCAT, NTS, PIEAS, GIKI, UET, FAST, NUST, and other competitive entrance examinations. By practicing these 250 MCQs and the Top 50 Challenging MCQs Quiz, you will develop a strong understanding of fluid mechanics, improve your numerical problem-solving ability, enhance logical reasoning, and gain the confidence needed to excel in objective-type Physics examinations.

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Fluid Dynamics

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MCQs No. 101

The equation of continuity for an incompressible fluid is:

a. $P+\frac{1}{2}\rho v^2+\rho gh=\text{constant}$

b. $A_1v_1=A_2v_2$

c. $F=ma$

d. $PV=\text{constant}$

The Correct Answer is option b. $A_1v_1=A_2v_2$

Explanation:
The continuity equation states that for an incompressible fluid, the product of cross-sectional area and velocity remains constant throughout the flow.

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MCQs No. 102

Water flows through a pipe of cross-sectional area 4 cm² with a speed of 2 m/s. What is the volume flow rate?

a. $4\times10^{-4}\,m^3/s$

b. $8\times10^{-4}\,m^3/s$

c. $2\times10^{-4}\,m^3/s$

d. $1.6\times10^{-3}\,m^3/s$

The Correct Answer is option b. $8\times10^{-4}\,m^3/s$

Explanation:
Area = $4\,cm^2=4\times10^{-4}\,m^2$

$Q=Av=(4\times10^{-4})(2)=8\times10^{-4}\,m^3/s$

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MCQs No. 103

A pipe narrows from 8 cm² to 2 cm². If the speed of water in the wider section is 3 m/s, its speed in the narrower section is:

a. 6 m/s

b. 9 m/s

c. 12 m/s

d. 24 m/s

The Correct Answer is option c. 12 m/s

Explanation:
Using the continuity equation,

$A_1v_1=A_2v_2$

$8\times3=2\times v_2$

$v_2=12\,m/s$ 

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MCQs No. 104

If the cross-sectional area of a pipe is doubled, the speed of an incompressible fluid becomes:

a. Double

b. Half

c. Four times

d. Unchanged

The Correct Answer is option b. Half

Explanation:
Velocity is inversely proportional to area according to the continuity equation.

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MCQs No. 105

The SI unit of mass flow rate is:

a. kg/s

b. m³/s

c. N/s

d. Pa/s

The Correct Answer is option a. kg/s

Explanation:
Mass flow rate is measured in kilograms per second.

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MCQs No. 106

The mass flow rate of a fluid is expressed by:

a. $Av$ 

b. $\rho Av$

c. $\rho gh$ 

d. $\frac{1}{2}\rho v^2$ 

The Correct Answer is option b. $\rho Av$ 

Explanation:
Mass flow rate equals density × area × velocity.

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MCQs No. 107

Bernoulli's equation is valid only when the flow is:

a. Steady, incompressible, and non-viscous

b. Turbulent and compressible

c. Rotational only

d. Highly viscous

The Correct Answer is option a. Steady, incompressible, and non-viscous

Explanation:
These assumptions are necessary for the application of Bernoulli's theorem.

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MCQs No. 108

In Bernoulli's equation, $\frac{1}{2}\rho v^2$ represents:

a. Pressure energy

b. Potential energy

c. Kinetic energy per unit volume

d. Heat energy

The Correct Answer is option c. Kinetic energy per unit volume

Explanation:
This term is called the dynamic pressure of the fluid.

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MCQs No. 109

A liquid flows horizontally through a pipe. If its speed doubles, its dynamic pressure becomes:

a. Half

b. Double

c. Four times

d. Eight times

The Correct Answer is option c. Four times

Explanation:
Dynamic pressure is proportional to $v^2$. Doubling the speed increases it fourfold.

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MCQs No. 110

The speed of water flowing through a pipe increases from 2 m/s to 8 m/s. The dynamic pressure increases by a factor of:

a. 2

b. 4

c. 8

d. 16

The Correct Answer is option d. 16

Explanation:
Since dynamic pressure varies as $v^2$,

$(8/2)^2=16$.

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MCQs No. 111

A Venturi meter measures fluid flow using the difference in:

a. Density

b. Temperature

c. Pressure

d. Volume

The Correct Answer is option c. Pressure

Explanation:
The pressure difference between the wider and narrower sections is used to calculate the flow rate.

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MCQs No. 112

If the pressure of a moving fluid decreases, its speed:

a. Decreases

b. Remains constant

c. Increases

d. Becomes zero

The Correct Answer is option c. Increases

Explanation:
According to Bernoulli's principle, lower pressure corresponds to higher speed.

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MCQs No. 113

The Reynolds number depends directly upon:

a. Fluid velocity

b. Fluid density

c. Pipe diameter

d. All of these

The Correct Answer is option d. All of these

Explanation:
Reynolds number increases with density, velocity, and characteristic length, but decreases with viscosity.

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MCQs No. 114

Which quantity decreases the Reynolds number?

a. Density

b. Velocity

c. Diameter

d. Viscosity

The Correct Answer is option d. Viscosity

Explanation:
Greater viscosity increases resistance to flow, thereby reducing the Reynolds number.

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MCQs No. 115

If the velocity of a fluid doubles while all other quantities remain constant, the Reynolds number becomes:

a. Half

b. Double

c. Four times

d. Unchanged

The Correct Answer is option b. Double

Explanation:
Reynolds number is directly proportional to velocity.

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MCQs No. 116

Which of the following is most likely to produce turbulent flow?

a. Low velocity

b. Small pipe diameter

c. High Reynolds number

d. High viscosity

The Correct Answer is option c. High Reynolds number

Explanation:
Large Reynolds numbers indicate that inertial forces dominate over viscous forces, leading to turbulence.

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MCQs No. 117

The speed of efflux from a tank containing water at a depth of 5 m is approximately (g = 9.8 m/s²):

a. 5 m/s

b. 7 m/s

c. 9.9 m/s

d. 14 m/s

The Correct Answer is option c. 9.9 m/s

Explanation:
Using Torricelli's theorem,

$v=\sqrt{2gh}=\sqrt{2\times9.8\times5}\approx9.9\,m/s$

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MCQs No. 118

If the depth of water above a hole is quadrupled, the speed of efflux becomes:

a. Double

b. Four times

c. Half

d. Unchanged

The Correct Answer is option a. Double

Explanation:
Since $v=\sqrt{2gh}$, 

speed is proportional to the square root of depth.

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MCQs No. 119

Which factor has the greatest effect on drag force in turbulent flow?

a. Velocity²

b. Density only

c. Radius only

d. Temperature only

The Correct Answer is option a. Velocity²

Explanation:
In turbulent flow, drag force is approximately proportional to the square of the velocity.

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MCQs No. 120

A small steel sphere falls through glycerin. Which force increases until terminal velocity is reached?

a. Weight

b. Buoyant force

c. Drag force

d. Magnetic force

The Correct Answer is option c. Drag force

Explanation:
As the sphere speeds up, the viscous drag increases until it balances the effective weight, after which the sphere moves with constant terminal velocity.

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MCQs No. 121

Water flows through a horizontal pipe where the speed increases from 2 m/s to 6 m/s. According to Bernoulli's principle, the pressure in the second section will:

a. Increase

b. Remain unchanged

c. Decrease

d. Become zero

The Correct Answer is option c. Decrease

Explanation:
In a horizontal pipe, an increase in fluid velocity results in a decrease in pressure according to Bernoulli's equation.

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MCQs No. 122

A liquid flows through a pipe whose diameter is reduced to half. The velocity of the liquid becomes:

a. Half

b. Double

c. Four times

d. Eight times

The Correct Answer is option c. Four times

Explanation:
Area is proportional to the square of diameter. If the diameter becomes half, the area becomes one-fourth. Therefore, the velocity becomes four times to satisfy the continuity equation.

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MCQs No. 123

A pipe has a cross-sectional area of 6 × 10⁻⁴ m². If water flows at 5 m/s, the volume flow rate is:

a. 1.5 × 10⁻³ m³/s

b. 3 × 10⁻³ m³/s

c. 5 × 10⁻³ m³/s

d. 6 × 10⁻³ m³/s

The Correct Answer is option b. 3 × 10⁻³ m³/s

Explanation:
Using $Q=Av$

$Q=(6\times10^{-4})(5)=3\times10^{-3}\,m^3/s$

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MCQs No. 124

The density of water is 1000 kg/m³. If its volume flow rate is 0.004 m³/s, the mass flow rate is:

a. 2 kg/s

b. 4 kg/s

c. 40 kg/s

d. 400 kg/s

The Correct Answer is option b. 4 kg/s

Explanation:
Mass flow rate = ρQ

= 1000 × 0.004

= 4 kg/s.

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MCQs No. 125

A liquid enters a pipe at a speed of 3 m/s through an area of 10 cm². If the outlet area is 5 cm², the outlet speed is:

a. 1.5 m/s

b. 3 m/s

c. 6 m/s

d. 12 m/s

The Correct Answer is option c. 6 m/s

Explanation:
Applying the continuity equation,

$10\times3=5\times v$

Therefore,

$v=6\,m/s$

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MCQs No. 126

Which quantity remains constant in Bernoulli's equation for an ideal fluid?

a. Pressure only

b. Velocity only

c. Total mechanical energy per unit volume

d. Height only

The Correct Answer is option c. Total mechanical energy per unit volume

Explanation:
The sum of pressure energy, kinetic energy, and potential energy per unit volume remains constant along a streamline.

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MCQs No. 127

If the velocity of an ideal fluid becomes three times greater, the dynamic pressure becomes:

a. Three times

b. Six times

c. Nine times

d. Twenty-seven times

The Correct Answer is option c. Nine times

Explanation:
Dynamic pressure is proportional to $v^2$. Therefore,

$3^2=9$.

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MCQs No. 128

The Reynolds number for a flowing liquid increases when:

a. Velocity decreases

b. Viscosity increases

c. Pipe diameter increases

d. Density decreases

The Correct Answer is option c. Pipe diameter increases

Explanation:
Reynolds number is directly proportional to the characteristic diameter of the pipe.

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MCQs No. 129

A high Reynolds number indicates that:

a. Viscous forces dominate

b. Flow is certainly laminar

c. Inertial forces dominate

d. Fluid is incompressible

The Correct Answer is option c. Inertial forces dominate

Explanation:
Large Reynolds numbers indicate that inertial forces are much greater than viscous forces, making turbulent flow more likely.

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MCQs No. 130

Which quantity has the same SI unit as pressure?

a. Dynamic pressure

b. Density

c. Velocity

d. Volume flow rate

The Correct Answer is option a. Dynamic pressure

Explanation:
Dynamic pressure ($\frac{1}{2}\rho v^2$ ) is also measured in pascals (Pa).

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MCQs No. 131

Water emerges from an opening at the bottom of a tank. If the depth of water is increased from 2 m to 8 m, the speed of efflux becomes:

a. Double

b. Four times

c. Half

d. Eight times

The Correct Answer is option a. Double

Explanation:
Since $v=\sqrt{2gh}$

$\sqrt{\frac{8}{2}}=\sqrt4=2$

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MCQs No. 132

A Venturi meter works because the pressure at the narrow section is:

a. Greater than at the wider section

b. Equal to atmospheric pressure

c. Less than at the wider section

d. Always zero

The Correct Answer is option c. Less than at the wider section

Explanation:
The increased velocity in the narrow section causes the pressure to decrease.

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MCQs No. 133

According to Stokes' law, drag force is directly proportional to:

a. Radius of the sphere

b. Velocity of the sphere

c. Coefficient of viscosity

d. All of these

The Correct Answer is option d. All of these

Explanation:
Stokes' law states:

$F=6\pi\eta rv$,

so drag depends on viscosity, radius, and velocity.

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MCQs No. 134

The drag force acting on a sphere doubles if its speed is doubled under laminar flow because drag is proportional to:

a. $v^2$

b. $v$

c. $\sqrt v$

d. $1/v$

The Correct Answer is option b. $v$

Explanation:
Stokes' law applies in laminar flow where drag varies directly with velocity.

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MCQs No. 135

Which of the following increases the terminal velocity of a sphere moving through a liquid?

a. Increasing viscosity

b. Decreasing radius

c. Increasing radius

d. Increasing fluid density only

The Correct Answer is option c. Increasing radius

Explanation:
Terminal velocity is directly proportional to the square of the sphere's radius.

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MCQs No. 136

A skydiver opens a parachute. The terminal velocity decreases mainly because:

a. Gravity decreases

b. Air density becomes zero

c. Drag force increases greatly

d. Body mass increases

The Correct Answer is option c. Drag force increases greatly

Explanation:
The parachute greatly increases surface area, producing a much larger drag force.

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MCQs No. 137

Which of the following provides the least resistance while moving through air?

a. Flat plate

b. Cube

c. Sphere

d. Streamlined body

The Correct Answer is option d. Streamlined body

Explanation:
A streamlined body reduces turbulence and minimizes drag.

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MCQs No. 138

The lift force on an aircraft wing is produced because:

a. Air moves slower above the wing

b. Air pressure is greater above the wing

c. Air moves faster above the wing than below it

d. Gravity becomes smaller

The Correct Answer is option c. Air moves faster above the wing than below it

Explanation:
Higher air speed above the wing creates lower pressure, producing lift.

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MCQs No. 139

Which equation is mainly used to calculate the speed of liquid leaving a hole in a tank?

a. Newton's Second Law

b. Continuity Equation

c. Torricelli's Theorem

d. Boyle's Law

The Correct Answer is option c. Torricelli's Theorem

Explanation:
Torricelli's theorem gives the speed of efflux as $v=\sqrt{2gh}$

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MCQs No. 140

A student increases the velocity of water flowing through a pipe while keeping its density and area constant. Which quantity increases directly?

a. Volume flow rate

b. Dynamic pressure

c. Reynolds number

d. All of these

The Correct Answer is option d. All of these

Explanation:
Increasing velocity increases the volume flow rate ($Q=Av$), Reynolds number ($Re\propto v$), and dynamic pressure ($\frac{1}{2}\rho v^2$). However, dynamic pressure increases with the square of velocity, while the other two increase directly with velocity.

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MCQs No. 141

Water flows through a horizontal pipe. If the velocity of water increases, the pressure of the water:

a. Increases

b. Remains constant

c. Decreases

d. First increases and then decreases

The Correct Answer is option c. Decreases

Explanation:
According to Bernoulli's principle, an increase in the speed of an ideal fluid causes a decrease in its pressure.

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MCQs No. 142

The radius of a pipe is doubled. Keeping the volume flow rate constant, the velocity of the fluid becomes:

a. Double

b. Half

c. One-fourth

d. One-sixteenth

The Correct Answer is option c. One-fourth

Explanation:
Since the cross-sectional area is proportional to the square of the radius, doubling the radius increases the area four times. Therefore, the velocity becomes one-fourth.

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MCQs No. 143

A pipe has a diameter of 4 cm. If its diameter is reduced to 2 cm, the velocity of an incompressible fluid becomes:

a. Twice

b. Three times

c. Four times

d. Eight times

The Correct Answer is option c. Four times

Explanation:
Halving the diameter reduces the area to one-fourth. According to the continuity equation, the velocity therefore becomes four times greater.

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MCQs No. 144

The pressure energy per unit volume of a fluid has the same SI unit as:

a. Velocity

b. Force

c. Pressure

d. Density

The Correct Answer is option c. Pressure

Explanation:
Pressure energy per unit volume is simply pressure, measured in pascals (Pa).

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MCQs No. 145

If the density of a moving fluid doubles while its velocity remains unchanged, the dynamic pressure becomes:

a. Half

b. Double

c. Four times

d. Unchanged

The Correct Answer is option b. Double

Explanation:
Dynamic pressure is given by $\frac{1}{2}\rho v^2$ . Therefore, doubling the density doubles the dynamic pressure.

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MCQs No. 146

The value of Reynolds number becomes larger when the:

a. Viscosity increases

b. Velocity decreases

c. Fluid velocity increases

d. Pipe diameter decreases

The Correct Answer is option c. Fluid velocity increases

Explanation:
Reynolds number is directly proportional to the velocity of the fluid.

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MCQs No. 147

Which combination is most likely to produce laminar flow?

a. High velocity and low viscosity

b. High Reynolds number

c. Low velocity and high viscosity

d. Large pipe diameter and high speed

The Correct Answer is option c. Low velocity and high viscosity

Explanation:
Laminar flow occurs when viscous forces dominate over inertial forces, corresponding to a low Reynolds number.

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MCQs No. 148

A liquid flows through a Venturi meter. At the throat of the Venturi tube, the liquid has:

a. Maximum pressure and minimum speed

b. Minimum pressure and maximum speed

c. Maximum pressure and maximum speed

d. Equal pressure and speed

The Correct Answer is option b. Minimum pressure and maximum speed

Explanation:
The narrow throat increases the fluid's speed and decreases its pressure according to Bernoulli's principle.

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MCQs No. 149

The density of water is 1000 kg/m³. If the velocity is 4 m/s, the dynamic pressure is:

a. 2000 Pa

b. 4000 Pa

c. 8000 Pa

d. 16000 Pa

The Correct Answer is option c. 8000 Pa

Explanation:
Dynamic pressure

$=\frac{1}{2}\rho v^2$

$=\frac{1}{2}(1000)(4^2)$

$=8000\ Pa$.

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MCQs No. 150

The drag force acting on a sphere moving through a viscous fluid depends upon:

a. Radius only

b. Velocity only

c. Viscosity only

d. Radius, velocity, and viscosity

The Correct Answer is option d. Radius, velocity, and viscosity

Explanation:
According to Stokes' law,

$F=6\pi\eta rv$ ,

the drag force depends on all three quantities.

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MCQs No. 151

A steel ball falls through oil and finally moves with constant speed because:

a. Gravity disappears

b. Oil stops exerting resistance

c. Drag force balances the effective weight

d. The ball loses its mass

The Correct Answer is option c. Drag force balances the effective weight

Explanation:
At terminal velocity, the upward drag force equals the effective weight of the ball, resulting in zero acceleration.

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MCQs No. 152

If the viscosity of a liquid is doubled, the terminal velocity of a falling sphere will:

a. Double

b. Become four times

c. Become half

d. Remain unchanged

The Correct Answer is option c. Become half

Explanation:
Terminal velocity is inversely proportional to the coefficient of viscosity.

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MCQs No. 153

Which one of the following quantities is inversely proportional to viscosity?

a. Drag force

b. Reynolds number

c. Pressure

d. Density

The Correct Answer is option b. Reynolds number

Explanation:
Reynolds number decreases as viscosity increases because viscous forces become more significant.

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MCQs No. 154

The speed of efflux from a hole depends upon:

a. Density of the liquid only

b. Area of the opening only

c. Depth of the liquid above the opening

d. Shape of the container

The Correct Answer is option c. Depth of the liquid above the opening

Explanation:
According to Torricelli's theorem,

$v=\sqrt{2gh}$

where, $h$  is the depth of the liquid above the hole.

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MCQs No. 155

The speed of efflux from a tank is 14 m/s. The approximate height of water above the opening is (g = 9.8 m/s²):

a. 5 m

b. 10 m

c. 14 m

d. 20 m

The Correct Answer is option b. 10 m

Explanation:
Using

$h=\frac{v^2}{2g}=\frac{196}{19.6}=10\ m$

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MCQs No. 156

Which statement correctly describes streamline flow?

a. Fluid particles cross one another repeatedly.

b. Adjacent layers move smoothly without mixing.

c. Velocity changes randomly in every direction.

d. Numerous eddies are formed.

The Correct Answer is option b. Adjacent layers move smoothly without mixing.

Explanation:
In streamline (laminar) flow, fluid particles move in smooth, parallel paths.

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MCQs No. 157

A racing car is designed with a streamlined body mainly to:

a. Increase air pressure

b. Reduce air resistance

c. Increase its weight

d. Reduce engine power

The Correct Answer is option b. Reduce air resistance

Explanation:
A streamlined design minimizes drag, improving speed and fuel efficiency.

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MCQs No. 158

Which application mainly depends upon the pressure difference produced by high-speed air?

a. Electric iron

b. Atomizer

c. Ammeter

d. Transformer

The Correct Answer is option b. Atomizer

Explanation:
An atomizer uses fast-moving air to create a low-pressure region that draws liquid upward and sprays it.

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MCQs No. 159

Which instrument uses Bernoulli's principle to determine the discharge of a fluid through a pipe?

a. Vernier caliper

b. Micrometer screw gauge

c. Venturi meter

d. Hydrometer

The Correct Answer is option c. Venturi meter

Explanation:
The Venturi meter measures fluid flow rate by utilizing the pressure difference between two sections of a pipe.

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MCQs No. 160

A body moving through a fluid experiences minimum drag when it is:

a. Rough and flat

b. Large and irregular

c. Streamlined

d. Cubical

The Correct Answer is option c. Streamlined

Explanation:
A streamlined body allows the fluid to flow smoothly around it, greatly reducing drag force.

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MCQs No. 161

Water flows through a horizontal pipe whose diameter decreases from 8 cm to 4 cm. If the velocity in the wider section is 2 m/s, the velocity in the narrower section is:

a. 4 m/s

b. 6 m/s

c. 8 m/s

d. 10 m/s

The Correct Answer is option c. 8 m/s

Explanation:
Since the diameter is halved, the cross-sectional area becomes one-fourth. Using the continuity equation,

$$A_1v_1=A_2v_2$$
$$v_2=4\times2=8\,m/s$$

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MCQs No. 162

The cross-sectional area of a pipe is 0.02 m² and water flows at 4 m/s. The volume flow rate is:

a. 0.02 m³/s

b. 0.04 m³/s

c. 0.08 m³/s

d. 0.16 m³/s

The Correct Answer is option c. 0.08 m³/s

Explanation:
Using

$$Q=Av$$
$$Q=(0.02)(4)=0.08\,m^3/s$$

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MCQs No. 163

The density of water is 1000 kg/m³. If the volume flow rate is 0.08 m³/s, the mass flow rate is:

a. 8 kg/s

b. 40 kg/s

c. 80 kg/s

d. 800 kg/s

The Correct Answer is option c. 80 kg/s

Explanation:
Mass flow rate

$$=\rho Q$$
$$=1000\times0.08=80\,kg/s$$

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MCQs No. 164

If the velocity of an ideal fluid becomes four times greater, its kinetic energy per unit volume becomes:

a. Four times

b. Eight times

c. Sixteen times

d. Sixty-four times

The Correct Answer is option c. Sixteen times

Explanation:
Since kinetic energy per unit volume is

$$\frac12\rho v^2,$$

it varies as the square of velocity.

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MCQs No. 165

The dynamic pressure of water moving at 6 m/s is approximately (ρ = 1000 kg/m³):

a. 6000 Pa

b. 9000 Pa

c. 18000 Pa

d. 36000 Pa

The Correct Answer is option c. 18000 Pa

Explanation:

$$\frac12\rho v^2 =\frac12(1000)(36) =18000\,Pa$$

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MCQs No. 166

The Reynolds number will decrease if:

a. Velocity increases

b. Diameter increases

c. Viscosity increases

d. Density increases

The Correct Answer is option c. Viscosity increases

Explanation:
Since

$$Re=\frac{\rho vd}{\eta},$$

Reynolds number is inversely proportional to viscosity.

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MCQs No. 167

A Reynolds number much smaller than the critical value indicates:

a. Highly turbulent flow

b. Laminar flow

c. Supersonic flow

d. Compressible flow

The Correct Answer is option b. Laminar flow

Explanation:
Small Reynolds numbers indicate that viscous forces dominate, resulting in smooth streamline flow.

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MCQs No. 168

A fluid moving at high speed over the upper surface of an aerofoil produces:

a. High pressure

b. Low pressure

c. Constant pressure

d. Zero pressure

The Correct Answer is option b. Low pressure

Explanation:
According to Bernoulli's principle, higher velocity produces lower pressure, generating lift.

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MCQs No. 169

The lift acting on an aircraft is mainly proportional to the:

a. Pressure difference across the wing

b. Weight of the aircraft

c. Engine power only

d. Thickness of the wing only

The Correct Answer is option a. Pressure difference across the wing

Explanation:
The pressure difference between the upper and lower surfaces of the wing produces lift.

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MCQs No. 170

The speed of efflux from a tank is 7 m/s. The corresponding depth of water is approximately (g = 9.8 m/s²):

a. 1.5 m

b. 2.5 m

c. 5 m

d. 7 m

The Correct Answer is option b. 2.5 m

Explanation:

$$h=\frac{v^2}{2g} =\frac{49}{19.6} =2.5\,m$$

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MCQs No. 171

If the depth of liquid in a tank becomes nine times greater, the speed of efflux becomes:

a. Three times

b. Nine times

c. Eighteen times

d. One-third

The Correct Answer is option a. Three times

Explanation:
Since

$$v\propto\sqrt{h},$$

increasing the depth by a factor of 9 increases the speed by a factor of 3.

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MCQs No. 172

According to Stokes' law, if the radius of a sphere doubles while velocity remains constant, the drag force becomes:

a. Half

b. Double

c. Four times

d. Eight times

The Correct Answer is option b. Double

Explanation:
Since

$$F=6\pi\eta rv,$$

drag force is directly proportional to the radius.

---

MCQs No. 173

The terminal velocity of a sphere is directly proportional to:

a. Radius

b. Radius²

c. Radius³

d. Radius⁴

The Correct Answer is option b. Radius²

Explanation:
Terminal velocity increases with the square of the sphere's radius according to Stokes' law.

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MCQs No. 174

A parachute reduces the speed of a skydiver mainly by increasing:

a. Weight

b. Air pressure

c. Drag force

d. Gravity

The Correct Answer is option c. Drag force

Explanation:
The large surface area of the parachute greatly increases air resistance.

---

MCQs No. 175

The viscosity of most liquids decreases because:

a. Molecular attraction decreases with temperature

b. Density becomes zero

c. Pressure becomes constant

d. Velocity increases

The Correct Answer is option a. Molecular attraction decreases with temperature

Explanation:
Heating weakens intermolecular forces, allowing the liquid to flow more easily.

---

MCQs No. 176

The viscosity of gases generally increases because:

a. Molecular collisions increase with temperature

b. Density decreases

c. Gravity increases

d. Pressure becomes zero

The Correct Answer is option a. Molecular collisions increase with temperature

Explanation:
Higher temperatures increase molecular motion, increasing the momentum transfer between gas layers.

---

MCQs No. 177

Which instrument directly uses the pressure difference produced by varying fluid velocity?

a. Barometer

b. Hydrometer

c. Venturi meter

d. Stopwatch

The Correct Answer is option c. Venturi meter

Explanation:
A Venturi meter determines the discharge of a fluid by measuring pressure differences.

---

MCQs No. 178

The operation of a carburetor in an automobile is mainly based on:

a. Pascal's law

b. Bernoulli's principle

c. Newton's law

d. Hooke's law

The Correct Answer is option b. Bernoulli's principle

Explanation:
Fast-moving air produces low pressure, drawing fuel into the airflow.

---

MCQs No. 179

Which one of the following devices does NOT operate on Bernoulli's principle?

a. Atomizer

b. Venturi meter

c. Filter pump

d. Hydraulic press

The Correct Answer is option d. Hydraulic press

Explanation:
A hydraulic press works on Pascal's law, whereas the others use Bernoulli's principle.

---

MCQs No. 180

A streamlined body moving through a fluid experiences less drag because it:

a. Increases turbulence

b. Reduces flow separation and eddies

c. Increases pressure behind the body

d. Increases its weight

The Correct Answer is option b. Reduces flow separation and eddies

Explanation:
Streamlining allows fluid to flow smoothly around the body, minimizing eddies and drag.

---

MCQs No. 181

Water flows through a horizontal pipe whose diameter changes from 10 cm to 5 cm. If the velocity in the wider section is 1.5 m/s, the velocity in the narrower section is:

a. 3 m/s

b. 4.5 m/s

c. 6 m/s

d. 9 m/s

The Correct Answer is option c. 6 m/s

Explanation:
The diameter is reduced to half, so the cross-sectional area becomes one-fourth. By the continuity equation,

$$A_1v_1=A_2v_2$$
$$v_2=4\times1.5=6\,m/s$$

---

MCQs No. 182

A pipe carries water with a cross-sectional area of 0.05 m² at a speed of 3 m/s. The volume flow rate is:

a. 0.05 m³/s

b. 0.10 m³/s

c. 0.15 m³/s

d. 0.30 m³/s

The Correct Answer is option c. 0.15 m³/s

Explanation:
Using

$$Q=Av=(0.05)(3)=0.15\,m^3/s$$

---

MCQs No. 183

The density of water is 1000 kg/m³. If the volume flow rate is 0.15 m³/s, the mass flow rate is:

a. 15 kg/s

b. 75 kg/s

c. 150 kg/s

d. 300 kg/s

The Correct Answer is option c. 150 kg/s

Explanation:
Mass flow rate

$$=\rho Q$$
$$=1000\times0.15=150\,kg/s$$

---

MCQs No. 184

The velocity of an ideal fluid becomes five times greater. Its dynamic pressure becomes:

a. Five times

b. Ten times

c. Twenty-five times

d. Fifty times

The Correct Answer is option c. Twenty-five times

Explanation:
Dynamic pressure is proportional to the square of velocity.

$$5^2=25$$

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MCQs No. 185

Water flows at 8 m/s. The dynamic pressure is approximately (ρ = 1000 kg/m³):

a. 8,000 Pa

b. 16,000 Pa

c. 24,000 Pa

d. 32,000 Pa

The Correct Answer is option d. 32,000 Pa

Explanation:

$$\frac12\rho v^2 =\frac12(1000)(8^2) =32,000\,Pa$$

---

MCQs No. 186

If the coefficient of viscosity of a liquid is reduced to one-half while all other quantities remain unchanged, the Reynolds number becomes:

a. Half

b. Double

c. Four times

d. Unchanged

The Correct Answer is option b. Double

Explanation:
Since

$$Re=\frac{\rho vd}{\eta},$$

Reynolds number is inversely proportional to viscosity.

---

MCQs No. 187

Which condition is most suitable for obtaining turbulent flow?

a. Low Reynolds number

b. High viscosity and low velocity

c. High velocity and large pipe diameter

d. Small diameter and high viscosity

The Correct Answer is option c. High velocity and large pipe diameter

Explanation:
A high velocity and large diameter increase the Reynolds number, making turbulent flow more likely.

---

MCQs No. 188

A fluid moves from a wider section to a narrower section of a horizontal pipe. Which quantity remains unchanged?

a. Pressure

b. Velocity

c. Mass flow rate

d. Dynamic pressure

The Correct Answer is option c. Mass flow rate

Explanation:
According to the continuity equation, the mass flow rate remains constant throughout steady flow.

---

MCQs No. 189

The speed of efflux from a tank is 14 m/s. If the depth of water is doubled, the new speed will be approximately:

a. 14 m/s

b. 19.8 m/s

c. 28 m/s

d. 39.6 m/s

The Correct Answer is option b. 19.8 m/s

Explanation:
Since

$$v\propto\sqrt{h},$$

doubling the depth increases the speed by

$$\sqrt2.$$
$$14\times1.414\approx19.8\,m/s$$

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MCQs No. 190

The speed of efflux of water from a tank is 9.9 m/s. The height of water above the hole is approximately (g = 9.8 m/s²):

a. 2.5 m

b. 5 m

c. 7.5 m

d. 10 m

The Correct Answer is option b. 5 m

Explanation:

$$h=\frac{v^2}{2g} =\frac{9.9^2}{19.6} \approx5\,m$$

---

MCQs No. 191

According to Stokes' law, if the radius and velocity of a sphere are both doubled, the drag force becomes:

a. Two times

b. Four times

c. Six times

d. Eight times

The Correct Answer is option b. Four times

Explanation:
Since

$$F=6\pi\eta rv,$$

drag force is directly proportional to both radius and velocity.

$$2\times2=4$$

---

MCQs No. 192

The terminal velocity of a sphere moving through a liquid becomes four times greater if its radius becomes:

a. Double

b. Four times

c. Eight times

d. Sixteen times

The Correct Answer is option a. Double

Explanation:
Terminal velocity is proportional to the square of the radius.

$$(2)^2=4$$

---

MCQs No. 193

Which factor does NOT directly affect the terminal velocity of a falling sphere?

a. Radius of the sphere

b. Viscosity of the liquid

c. Density difference

d. Colour of the sphere

The Correct Answer is option d. Colour of the sphere

Explanation:
Terminal velocity depends on the sphere's size, densities, and the viscosity of the liquid, but not on its colour.

---

MCQs No. 194

An airplane wing generates lift because the pressure is:

a. Greater above the wing

b. Smaller above the wing

c. Equal on both sides

d. Zero above the wing

The Correct Answer is option b. Smaller above the wing

Explanation:
Air flows faster over the upper surface, reducing pressure and producing lift.

---

MCQs No. 195

A streamlined shape mainly reduces:

a. Gravitational force

b. Electrostatic force

c. Drag force

d. Buoyant force

The Correct Answer is option c. Drag force

Explanation:
Streamlining minimizes fluid resistance by reducing turbulence and eddies.

---

MCQs No. 196

A carburetor supplies fuel to an engine because fast-moving air creates:

a. High pressure

b. Low pressure

c. High temperature

d. High density

The Correct Answer is option b. Low pressure

Explanation:
The pressure difference caused by fast-moving air draws fuel into the air stream.

---

MCQs No. 197

The Venturi meter is mainly based on the combination of:

a. Newton's law and Hooke's law

b. Continuity equation and Bernoulli's principle

c. Pascal's law and Archimedes' principle

d. Ohm's law and Kirchhoff's law

The Correct Answer is option b. Continuity equation and Bernoulli's principle

Explanation:
The continuity equation relates velocity changes, while Bernoulli's principle relates the corresponding pressure changes.

---

MCQs No. 198

Which of the following is an example of reducing drag by streamlining?

a. A parachute

b. A racing bicycle helmet

c. A flat wooden board

d. A square box

The Correct Answer is option b. A racing bicycle helmet

Explanation:
A streamlined helmet allows air to flow smoothly around the cyclist, reducing air resistance.

---

MCQs No. 199

Which one of the following statements is correct for an ideal fluid in steady flow?

a. Pressure always remains constant.

b. Total mechanical energy remains constant along a streamline.

c. Velocity is zero everywhere.

d. Density continuously changes.

The Correct Answer is option b. Total mechanical energy remains constant along a streamline.

Explanation:
Bernoulli's equation states that the sum of pressure, kinetic, and potential energies per unit volume remains constant along a streamline.

---

MCQs No. 200

A student wants to maximize the speed of water flowing through a pipe without changing the flow rate. The best method is to:

a. Increase the diameter of the pipe

b. Decrease the diameter of the pipe

c. Increase the density of water

d. Increase the viscosity of water

The Correct Answer is option b. Decrease the diameter of the pipe

Explanation:
According to the continuity equation, reducing the cross-sectional area increases the velocity of the fluid while maintaining the same flow rate.

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