Mechanical Engineering Important MCQ (Qustions on Fluid Dynamics)

1) Shear stress in a turbulent flow is given by the formula
τ = η (du / dy)
Where η (eta) is,
a. eddy viscosity
b. apparent viscosity
c. virtual viscosity
d. all of the above
ANSWER: all of the above
2) Magnitude of eddy viscosity for laminar flow is
a. less than zero
b. zero
c. greater than zero
d. unpredictable
ANSWER: zero
3) Kinematic eddy viscosity (ε) is the ratio of
a. eddy viscosity (η) to dynamic viscosity (μ)
b. eddy viscosity (η) to kinematic viscosity (ν)
c. kinematic viscosity to eddy viscosity (η)
d. eddy viscosity (η) to mass density (ρ)
ANSWER: eddy viscosity (η) to mass density (ρ)
4) Friction factor for laminar flow is given by
a. (Re /64)
b. (64 / Re)
c. (Re / 16)
d. (16 / Re)
ANSWER: (64 / Re)
5) What is temporal mean velocity?
a. The average of velocities at a point over a certain period of time
b. The average of velocities of a single particle over different locations in a fluid flow
c. None of the abov
ANSWER: The average of velocities at a point over a certain period of time
6) The friction factor in fluid flowing through pipe depends upon
a. Reynold's number
b. relative roughness of pipe surface
c. both a. and b.
d. none of the above
ANSWER: both a. and b.
7) What is the effect of change in Reynold's number on friction factor in turbulent flow?
a. As the Reynold's number increases the friction factor increases in turbulent flow
b. As the Reynold's number increases the friction factor decreases in turbulent flow
c. change in Reynold's number does not affect the friction factor in turbulent flow
d. unpredictable
ANSWER: As the Reynold's number increases the friction factor decreases in turbulent
flow
8) What is the formula for determining the size of equivalent pipe for two pipes of lengths
L1, L2 and diameters d1, d2 respectively?
Where,
L = L1 + L2
a. (L / d) = (L1 / d1) + (L2 / d2)
b. (L / d2 ) = (L1 / d1
2) + (L2 / d2
2)
c. (L / d3) = (L1 / d1
3 ) + (L2 / d2
3)
d. (L / d5) = (L1 / d1
5 ) + (L2 / d2
5)
ANSWER: (L / d5) = (L1 / d1
5 ) + (L2 / d2
5)
9) What is a syphon?
a. A long bend pipe used to carry water from a reservoir at a higher level to another reservoir at a
lower level when two reservoirs are separated by a hill
b. A long bend pipe used to carry water from a reservoir at a lower level to another reservoir at a
higher level with some work input when two reservoirs are separated by a hill
c. A long bend pipe used to carry water from one reservoir to another reservoir when two
reservoirs are at same elevation
d. Unpredictable
ANSWER: A long bend pipe used to carry water from a reservoir at a higher level to
another reservoir at a lower level when two reservoirs are separated by a hill
10) The highest point of syphon is called as
a. syphon top
b. summit
c. reservoir
d. none of the above
ANSWER: summit
11) Match the following physical quantities in Group 1 with their dimensions in Group 2.
1. Work done (Energy) (W) ----------------------------- A. [M L 2 T – 3 ]
2. Power (P) ------------------------------------------------ B. [M L – 1 T – 1 ]
3. Momentum (M) ---------------------------------------- C. [M L 2 T – 2 ]
4. Modulus of elasticity (E) ----------------------------- D. [M L T – 1 ]
5. Dynamic viscosity (μ) --------------------------------- E. [M L – 1 T – 2 ]
a. 1-(C), 2-(A), 3-(D), 4-(E), 5-(B)
b. 1-(A), 2-(C), 3-(D), 4-(E), 5-(B)
c. 1-(C), 2-(A), 3-(E), 4-(B), 5-(D)
d. 1-(D), 2-(E), 3-(B), 4-(A), 5-(C)
ANSWER: 1-(C), 2-(A), 3-(D), 4-(E), 5-(B)
12) Which of the following equations is not dimensionally homogeneous?
Consider standard symbols for quantities.
a. (Force) F = m x a
b. (Head Loss due to friction) hf = (f L V2) / (2 g d)
c. (Torque) T = F x Distance
d. None of the above
ANSWER: None of the above
13) Which of the following is a dimensionless equation?
a. Reynold's equation
b. Euler's equation
c. Weber's equation
d. All of the above
ANSWER: All of the above
14) Which of the following number is applicable in open hydraulic structure such as
spillways, where gravitational force is predominant?
a. Reynold's Number
b. Euler's Number
c. Weber's Number
d. Froude's Number
ANSWER: Froude's Number
15) Square root of the ratio of inertia force to elastic force is called as
a. Mach's Number
b. Cauchy's Number
c. Both a. and b.
d. None of the above
ANSWER: Both a. and b.
16) Boundary layer thickness is the distance from the boundary to the point where
velocity of the fluid is
a. equal to 10% of free stream velocity
b. equal to 50% of free stream velocity
c. equal to 90% of free stream velocity
d. equal to 99% of free stream velocity
ANSWER: equal to 99% of free stream velocity
17) The component of the total force exerted by fluid on a body in the direction parallel to
the direction of motion is called as
a. lift
b. drag
c. both a. and b.
d. none of the above
ANSWER: drag
18) The sum of components of shear forces in the direction of flow of fluid is called as
a. shear drag
b. friction drag
c. skin drag
d. all of the above
ANSWER: all of the above
19) The body whose surface does not coincide with the streamline when places in a flow is
called as
a. streamline body
b. wave body
c. bluff body
d. induced body
ANSWER: bluff body
20) Which type of body is an airfoil?
a. streamline body
b. wave body
c. bluff body
d. induced body
ANSWER: streamline body
21) Bulk modulus is the ratio of
a. shear stress to volumetric strain
b. volumetric strain to shear stress
c. compressive stress to volumetric strain
d. volumetric strain to compressive stress
ANSWER: compressive stress to volumetric strain
22) When is a liquid said to be not in a boiling or vaporized state?
a. If the pressure on liquid is equal to its vapour pressure
b. If the pressure on liquid is less than its vapour pressure
c. If the pressure on liquid is more than its vapour pressure
d. Unpredictable
ANSWER: If the pressure on liquid is more than its vapour pressure
23) One litre of a certain fluid weighs 8N. What is its specific volume?
a. 2.03 x 10– 3 m3/kg
b. 20.3 x 10– 3 m3/kg
c. 12.3 x 10– 3 m3/kg
d. 1.23 x 10– 3 m3/kg
ANSWER: 1.23 x 10– 3 m3/kg
24) What is the correct formula for absolute pressure?
a. Pabs = Patm – Pgauge
b. Pabs = Pvacuum – Patm
c. Pabs = Pvacuum + Patm
d. Pabs = Patm+ Pgauge
ANSWER: Pabs = Patm+ Pgauge
25) According to Archimede's principle, if a body is immersed partially or fully in a fluid
then the buoyancy force is _______ the weight of fluid displaced by the body.
a. equal to
b. less than
c. more than
d. unpredictable
ANSWER: equal to

Questions on Fluid Mechanics (Mechanical Engineering Important MCQ)

1) Which of the following statements are true for dimensional analysis?
1. The functional relationship between dependent and non-dependent variables can be
expressed into dimensionless terms by dimensional analysis
2. In model testing, it reduces the number of variables into three numbers
3. It is used to change the theoretical equation into dimensionless form
4. It helps to convert the units of quantities from one system to another system
a. (1), (2) and (3)
b. (2), (3) and (4)
c. (1), (3) and (4)
d. (1), (2), (3) and (4)
ANSWER: (1), (2), (3) and (4)
2) The unit of physical quantity which does not depend on the unit of any other physical
quantity is called as
a. independent dimension
b. fundamental dimension
c. core dimension
d. none of the above
ANSWER: fundamental dimension
3) Which of the following is not a primary quantity?
a. Mass (M)
b. Temperature (θ)
c. Time (T)
d. None of the above
ANSWER: None of the above

4) What are the dimensions of force?
a. [M L T – 2 ]
b. [M L T – 1 ]
c. [M L 2 T – 2 ]
d. [M L 2 T 2 ]
ANSWER: [M L T – 2 ]
5) Which of the following quantities has the dimensions [M0 L0 T 0]
a. Density
b. Stress
c. Strain
d. Strain Rate
ANSWER: Strain
6) How is the intensity of shear stresses over the boundary layer?
a. small
b. large
c. sometimes small and sometimes large
d. cannot say
ANSWER: large
7) The velocity gradients over the boundary layer are
a. small
b. large
c. sometimes small and sometimes large
d. cannot say
ANSWER: large
8) What is the effect of free stream velocity on thickness of boundary layer?
a. Increase in free stream velocity increases the boundary layer thickness
b. Increase in free stream velocity decreases the boundary layer thickness
c. The boundary layer thickness does not get affected by any change in free stream velocity
d. unpredictable
ANSWER: Increase in free stream velocity decreases the boundary layer thickness
9) If viscosity of fluid is more, the thickness of boundary layer is
a. more
b. less
c. not affected by change in viscosity
d. unpredictable
ANSWER: more
10) The region in the turbulent boundary layer zone, adjacent to the solid surface of the
plate is called as
a. laminar sub layer
b. turbulent sub layer
c. solid sub layer
d. solid layer
ANSWER: laminar sub layer
11) Newton's law of viscosity states that
a. the shear stress applied to the fluid is directly proportional to the velocity gradient (du/dy)
b. the shear stress applied to the fluid is inversely proportional to the velocity gradient (du/dy)
c. the shear stress applied to the fluid is directly proportional to the specific weight of the fluid
d. the shear stress applied to the fluid is inversely proportional to the specific weight of the fluid
ANSWER: the shear stress applied to the fluid is directly proportional to the velocity
gradien
12) What is an ideal fluid?
a. A fluid which has no viscosity
b. A fluid which is incompressible
c. A fluid which has no surface tension
d. All of the above
ANSWER: All of the above
13) The below diagram is a graph of change in shear stress with respect to velocity
gradient in a fluid. What is a type of the fluid?



a. Newtonian fluid
b. Non-Newtonian fluid
c. Ideal fluid
d. Dilatent fluid
ANSWER: Non-Newtonian fluid
14) The fluid will rise in capillary when the capillary is placed in fluid, if
a. the adhesion force between molecules of fluid and tube is less than the cohesion between
liquid molecules
b. the adhesion force between molecules of fluid and tube is more than the cohesion between
liquid molecules
c. the adhesion force between molecules of fluid and tube is equal to the cohesion between liquid
molecules
d. cannot say
ANSWER: the adhesion force between molecules of fluid and tube is more than the
cohesion between liquid molecules
15) When the angle between surface tension with the liquid (θ) is greater than 90o, the
liquid becomes
a. flat
b. concave upward
c. convex upward
d. unpredictable
ANSWER: convex upward
16) If stream function (Ψ) satisfies the Laplace equation, it is a possible case of
a. a circular flow
b. a rotational flow
c. an irrotational flow
d. none of the above
ANSWER: an irrotational flow
17) Which acceleration has a nonzero value in uniform flow?
a. Local acceleration
b. Convective acceleration
c. Both local as well as convective acceleration
d. unpredictable
ANSWER: Local acceleration
18) Viscous forces are not present in
a. rotational flow
b. irrotational flow
c. laminar flow
d. none of the above
ANSWER: irrotational flow
19) The component of acceleration due to change in the direction of velocity vector is
called as
a. direction acceleration
b. tangential acceleration
c. normal acceleration
d. cannot say
ANSWER: normal acceleration
20) Blood circulation through arteries is
a. a laminar flow
b. a turbulent flow
ANSWER: a laminar flow
21) What is the correct formula for Euler's equation of motion?
Where,
ρ = density of the fluid
p = pressure force
g = acceleration due to gravity
v = velocity of the fluid
a. (∂p / ρ) + (∂g / ρ) + (∂v / ρ) = 0
b. (∂p / ρ) + (∂g / ρ) + (v dv) = 0
c. (∂p / ρ) + (g dz) + (v dv) = 0
d. (p dp) + (g dz) + (v dv) = 0
ANSWER: (∂p / ρ) + (g dz) + (v dv) = 0
22) Which of the following sentences are true for Bernoulli's equation?
1. Bernoulli's principle is applicable to ideal incompressible fluid
2. The gravity force and pressure forces are only considered in Bernoulli's principle
3. The flow of fluid is rotational for Bernoulli's principle
4. The heat transfer into or out of fluid should be zero to apply Bernoulli's principle
a. (1), (2) and (3)
b. (1), (3) and (4)
c. (1), (2) and (4)
d. (1), (2), (3) and (4)
ANSWER: (1), (2) and (4)
23) Which of the following devices does not use Bernoulli's equation as its working
principle?
a. Venturimeter
b. Orifice-meter
c. Pitot tube
d. None of the above
ANSWER: None of the above
24) Venturimeter consists of short converging conical tube which has a total inclination
angle of
a. 11 ± 1o
b. 21 ± 1o
c. 30 ± 1o
d. 60 ± 1o
ANSWER: 21 ± 1o
25) The cylindrical portion of short length, which connects converging and diverging
section of venturimeter, is called as
a. diffuser
b. connector
c. throat
d. manometer tube
ANSWER: throat

Topics for Group Discussion

1. Talk to the people or Talk to the Google - Pros and Cons
2. Is it the right time to have technology advancement in India, since technology advancement will reduce the number of jobs.
3. If you are asked to work on something that will help homeless road side people, what will it be?
4. Existence of invisible (not visible to naked eye) living beings in your surroundings.
5. Next Generation Gadgets
6. Mind travel - Do thoughts travel faster than light? 

Interview Questions with Answers

1. What is priming?

- Pump casing must be filled with liquid before the pump is started, or the pump will not be able to function. If the pump casing becomes filled with vapors or gases, the pump impeller becomes gas-bound and incapable of pumping.

2. Types of pumps?

- Positive Displacement

       - rotary lobe pump, progressive cavity pump, rotary gear pump, piston pump, diaphragm pump, screw pump, gear pump, Hydraulic pump, vane pump

- Centrifugal Pumps

        - end suction pumps, in-line pumps, double suction pumps, vertical multistage pumps, horizontal multistage pumps, submersible pumps, self-priming pumps, axial-flow pumps, regenerative pumps.

3. What is octane number in fuel?

- The octane rating of Gasoline is measured in a test engine, and is defined by comparison with the mixture of 2,2,4-trimethylpentane (iso-octane) and heptane which would have the same anti-knocking capacity as the fuel under test: the percentage, by volume, of 2,2,4-trimethylpentane in that mixture is the octane number of the fuel. For example, petrol with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90.

4. What is added in LPG to detect leakage?

- Methyl Mercaptan 

5. Pascal law ? Applications?

- Pascal's law or the Principle of transmission of fluid-pressure states that "pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure ratio (initial difference) remains the same.

Application- Hydraulic jacks, Car lifts, Fork Lifts

6. Can you transfer the heat energy from cold body to hot body?

- Yes, with external work. Eg : Air conditioner

7. What is hogging and sagging?

- Hogging and sagging describe the shape of a beam or similar long object when loading is applied. Hogging describes a beam which curves upwards in the middle, and sagging describes a beam which curves downwards.

8. What Bernoulli’s Principle?

- In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.

9. Difference between single acting and double acting pump?

- In single-acting machines the compression takes place on only one side of the piston; double-acting machines use both sides of the cylinder for compression. The flow is continuous in double acting and in single acting the flow is not continuous unless there is a surge vessel.

10. What is VSD?

- Variable Speed Drive

11. What is conduction, convection and radiation? Give Examples?

- Conduction or diffusion

The transfer of energy between objects that are in physical contact

Convection

The transfer of energy between an object and its environment, due to circular fluid motion

Radiation

The transfer of energy to or from a body by means of the emission or absorption of electromagnetic radiation

12. Mention flow measuring devices?

- Venturimeter, Rotameter etc.

13. Classify Carbon Steels on basis of carbon content?

Low-carbon steels contain up to 0.30% C. The largest category of this class of steel is flat-rolled products (sheet or strip), usually in the cold-rolled and annealed condition. The carbon content for these high-formability steels is very low, less than 0.10% C, with up to 0.4% Mn. Typical uses are in automobile body panels, tin plate, and wire products.
For rolled steel structural plates and sections, the carbon content may be increased to approximately 0.30%, with higher manganese content up to 1.5%. These materials may be used for stampings, forgings, seamless tubes, and boiler plate.
Medium-carbon steels are similar to low-carbon steels except that the carbon ranges from 0.30 to 0.60% and the manganese from 0.60 to 1.65%. Increasing the carbon content to approximately 0.5% with an accompanying increase in manganese allows medium carbon steels to be used in the quenched and tempered condition. The uses of medium carbon-manganese steels include shafts, axles, gears, crankshafts, couplings and forgings. Steels in the 0.40 to 0.60% C range are also used for rails, railway wheels and rail axles.
High-carbon steels contain from 0.60 to 1.00% C with manganese contents ranging from 0.30 to 0.90%. High-carbon steels are used for spring materials and high-strength wires.
Ultrahigh-carbon steels are experimental alloys containing 1.25 to 2.0% C. These steels are thermomechanically processed to produce microstructures that consist of ultrafine, equiaxed grains of spherical, discontinuous proeutectoid carbide particles.

14. Draw a possible isometric view for the object that has the following plan and elevation views?

 

Interview Questions with Answers

1. What happens to the diameter of a hole when a plate with a hole is heated uniformly?

- It increases.

2. Mention types of welding?

Arc welding, TIG welding, Gas metal arc welding, Flux-cored arc welding, Electro slag welding.

3. What is the difference between welding, soldering and brazing?

Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material (the weld pool) that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld

Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the workpiece

Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action.

 

4. What is yield point?

The yield strength or yield point is the stress at which a material begins to deform plastically.

5. What is shear stress?

A shear stress is defined as the component of stress coplanar with a material cross section. Shear stress arises from a force vector perpendicular to the surface normal vector of the cross section.

6.  Why there are holes or slots in the disc brakes in automobiles?

- To dissipate the enormous amount of heat generated while braking

7. How does a plane take off?

- Airspeed creates lift across the wings. The wings have a curvature, or camber, that increases the distance the air has to travel over the top of wing. This creates the Bernoulli effect. The Bernoulli Principle states that pressure in air decreases as the speed of the air increases. Faster air over the top of the wing lowers the pressure, and the difference created between the top and the bottom of the wing creates lift.

8. What are the types of boiler?

- Fire tube and Water Tube

9. What is a cantilever?

- A cantilever is a beam supported on only one end. The beam carries the load to the support where it is resisted by moment and shear stress. Cantilever construction allows for overhanging structures without external bracing. Cantilevers can also be constructed with trusses or slabs.

10. How will you extinguish an electrical fire?

- CO2

11. What is overdrive?

 Overdrive is a condition where the output of the transmission is revolving faster than the engine. Gear ratio is less than one.

12. Can the gear ratio be infinity?

- Yes. Eg: Rack and pinion. 

13. What is rack and pinion arrangement? Mention its application in day to day life?

- A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. Eg: CD drive, Steering Wheel 

14. What are left/right hand screws? Mention applications.

- Where the rotation of a shaft would cause a conventional right-handed nut to loosen rather than to tighten due to fretting induced precession. Examples include:

• The left hand pedal on a bicycle.
• The left-hand grinding wheel on a bench grinder.
• The lug nuts on the left side of some automobiles.

Mechanical Interview Questions and Answers

1. What is gear ratio?

A - gear ratio (gr) = (number of teeth on output or driven gear)/(number of teeth on input or driver gear)

Gear ratio can also be expressed as the relationship between the pitch circles of both wheels (where d is the pitch diameter of the input wheel and D is the pitch diameter of the output wheel):

2. What is pressure exerted by 1m of water column?

A – 0.1 Kg/cm2

3. What is anomalous expansion of water?

A - The maximum density of water occurs at 4 °C. It has the anomalous property of becoming less dense, not more, when it is cooled down to its solid form, ice. It expands to occupy 9% greater volume in this solid state, which accounts for the fact of ice floating on liquid water.4. What is unit of specific density of air.

4. What is unit of specific density of air?

A - Dimensionless

5. What is viscosity?

A - Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress.

6. What is Reynolds number?

A - In fluid mechanics, the Reynolds number Re is a dimensionless number that gives a measure of the ratio of inertial forces to viscous forces and consequently quantifies the relative importance of these two types of forces for given flow conditions.

7. What is Mach number?

Mach number (Ma or M) is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure. It is commonly used to represent the speed of an object when it is traveling close to or above the speed of sound.

8. What is the speed of sound?

- 340 m/s

9. During rainy season even though thunder occurs first followed by lightning; why do we see lightning first and then hear the thunder?

- Light travels faster than sound

10. What happens when you put petrol into the diesel engine?

- Petrol in a Diesel engine is actually worse. Petrol is a lot more likely to ignite under the conditions in a Diesel engine, but it'll ignite too soon and burn too fast compared to what the engine will expect. The crankshaft will not complete a full revolution and it shall knock. It might run, but very rough. The engine will be damaged very badly and life will be reduced. 

11. What is knocking?

- Knocking (also called knock, detonation, spark knock, pinging or pinking) in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.

12. What is the Zeroth law of thermodynamics?

- The zeroth law states that if two systems are in thermal equilibrium with a third system, they are also in thermal equilibrium with each other.

13. What is the 1^st, 2^nd and 3^rd law of thermodynamics?

• The first law of thermodynamics expresses the existence of a quantity called the internal energy of a system, and shows how it is related to the distinction between energy transfer as work and energy transfer as heat. The internal energy obeys the principle of conservation of energy but work and heat are not defined as separately conserved quantities. Equivalently, the first law of thermodynamics states that perpetual motion machines of the first kind are impossible.

• The second law of thermodynamics expresses the existence of a quantity called the entropy of a system and states that the entropy of an isolated macroscopic system never decreases, or, equivalently, that perpetual motion machines of the second kind are impossible.

• The third law of thermodynamics concerns the entropy of a perfect crystal at absolute zero temperature, and implies that it is impossible to cool a system to exactly absolute zero, or, equivalently, that perpetual motion machines of the third kind are impossible.

14. What is rankine cycle?

- The Rankine cycle is a cycle that converts heat into work. The heat is supplied externally to a closed loop, which usually uses water. This cycle generates about 80% of all electric power used throughout the world, including virtually all solar thermal, biomass, coal and nuclear power plants.

16. State the applications of compressor in day to day life?

- Air conditioners, Refrigerators

17. What is the function of foot valve in the well?

- It acts like a NRV. Prevents water flow back into the well and facilitates priming. 

18. What are the types of turbines?

- Impulse and Reaction

19. Why chimney is normally tapered?

- For draft

20. Which one cools faster – A square plate held horizontal or A square plate held vertical?

- Vertical. Because the radiation due to the bottom face of the horizontal face in turn heats the top surface of the plate.