Category: Fluid Mechanics Objective Questions

250+ TOP MCQs on Continuity Equation in Two and Three Dimensions and Answers

Fluid Mechanics Multiple Choice Questions on “Continuity Equation in Two and Three Dimensions”.

1. The continuity equation is based on the premise of-
a) Law of conservation of energy
b) Law of conservation of mass
c) Law of conservation of momentum
d) None of the mentioned
Answer: b
Clarification: Continuity equation is based on the the principle of conservation of mass.

2. The continuity equation is only applicable to incompressible fluid.
a) True
b) False
Answer: b
Clarification: The continuity equation is only applicable to incompressible as well as compressible fluid.

3. For incompressible fluid flow, if area reduces then what is the effect on the velocity.
a) increases
b) decreases
c) first increases then decreases
d) first decreases then increases
Answer: a
Clarification: According to continuity equation,
Area × velocity = constant
Hence, as area decreases velocity increases.

4. For compressible fluid flow in a pipe, having decrease in specific gravity what will be the effect of decrease in diameter?
a) It will cause increase in velocity
b) It will cause decrease in velocity
c) It remains constant
d) None of the mentioned
Answer: a
Clarification: According to continuity equation,
ρ*A*v = constant
Hence, as density and area decreases velocity is bound to increase.

5. What is the most common assumption while dealing with fluid flow problems using continuity equation?
a) Flow is assumed to be compressible
b) Flow is assumed to be unsteady
c) Flow is assumed to be steady
d) Flow is assumed to be turbulent
Answer: c
Clarification: In majority of the fluid flow problems, flow is assumed to be steady.

6. The diameters of a pipe at the sections 1 and 2 are 8 cm and 13 cm respectively. Find the discharge through pipe if the velocity of water flowing through the pipe at section 1 is 6 m/s. Determine also the velocity at section 2.
a) 2.27 m/s
b) 4.54 m/s
c) 1.13 m/s
d) 3.25 m/s
Answer: a
Clarification: According to continuity equation,
Area × velocity = constant
Area1*Velocity1 = Area2*Velocity2
Velocity2=(Area1*Velocity1)/Area2
= (82 * 6) / 132=2.27 m/s.

7. The continuity equation can only be used for analysis of conserved quantity.
a) True
b) False
Answer: a
Clarification: Continuity equation is defined on a control volume and hence, is applicable only to Conserved quantities.

8. The diameter of a pipe at the section 1 is 9 cm. If the velocity of water flowing through the pipe at section 1 is 4.8 m/s and section 2 is 9 m/s, Determine the area at section 2.
a) 33.93 m2
b) 67.86 m2
c) 16.96 m2
d) 38.66 m2
Answer: a
Clarification: According to continuity equation,
Area × velocity = constant
Area1*Velocity1 = Area2*Velocity2
(Area1*Velocity1)/Velocity2=Area2
Area 2= 33.93 m2.

9. For a flow to be physically possible it must primarily satisfy which equation?
a) Equation of conservation of energy
b) Equation of conservation of mass or continuity equation
c) Equation of conservation of momentum
d) None of the mentioned
Answer: a
Clarification: Fluid flow must satisfy equation of conservation of mass or continuity equation, for itto be physically possible.

10. Continuity equation can also be derived for polar coordinate system
a) True
b) False
Answer: a
Clarification: Continuity equation in polar coordinate is also used for analysis.

250+ TOP MCQs on Discharge Over different type of weirs and Answers

Fluid Mechanics Assessment Questions and Answers on “Discharge Over Broad-Crested Weir, Narrow Crested Weir, Ogee Weir, Submerged or Drowned Weir”.

1. In discharge of water over narrow crested weir, head of water is directly proportional to Discharge Coefficient.
a) True
b) False
Answer: b
Clarification: In discharge of water over narrow crested weir, head of water is inversely proportional to Discharge Coefficient.

2. In discharge of water over narrow crested weir, discharge is directly proportional to the cube root of acceleration due to gravity.
a) True
b) False
Answer: b
Clarification: In discharge of water over narrow crested weir, discharge is directly proportional to the square root of acceleration due to gravity.

3. In discharge of water over ogee weir, discharge is directly proportional to the second power of length.
a) True
b) False
Answer: b
Clarification: In discharge of water over ogee weir, discharge is directly proportional to the first power of length.

4. For discharge over ogee weir discharge is directly proportional to length but for discharge over narrow crested weir it is inversely proportional to length.
a) True
b) False
Answer: b
Clarification: For both weirs it’s same.

5. An Ogee weir 5 m long had a head of 40 cm of water. If CD = 0.61, find the discharge over the weir.
a) 2.9 m3/s
b) 2.3 m3/s
c) 3.1 m3/s
d) 3.3 m3/s
Answer: a
Clarification: Q = 0.67 * Cd * L * √2g * H1.5
Q = 2.3 m3/s.

6. The height of water on upstream and downstream side of a submerged weir of 4 m length are 24 cm and 13 cm. If Cd for free and drowned portions are .62 and .78 respectively, find the discharge over the weir.
a) .85 m3/s
b) 1.35 m3/s
c) 3.2 m3/s
d) .55 m3/s
Answer: a
Clarification: Q = 0.67 * Cd1 * L * √2g * H1.5 +. Cd2 * L * h * √2g(H – h)
= .67 * .6 * 3 * √2g * (.24 – .13)1.5 + .8 * 3 * .13 √2g(.24 – .13)
= .85 m3/s.

7. An Ogee weir 3.4 m long had a head of 40 cm of water. If CD = 0.63 find the discharge over the weir.
a) 1.61 m3/s
b) 2.5 m3/s
c) 3.1 m3/s
d) 3.3 m3/s
Answer: a
Clarification: Q = 0.67 * Cd * L * √2g * H1.5
Q = 1.61 m3/s.

8. The height of water on upstream and downstream side of a submerged weir of 4 m length are 23.5 cm and 14 cm. If Cd for free and drowned portions are .61 and .75 respectively, find the discharge over the weir.
a) m3/s
b) 1.35 m3/s
c) 3.2 m3/s
d) .55 m3/s
Answer: a
Clarification: Q = 0.67 * Cd1 * L * √2g * H1.5 +. Cd2 * L * h * √2g(H – h)
= .67 * .6 * 3 * √2g * (.24 – .13)1.5 + .8 * 3 * .13 √2g(.24 – .13)
= .85 m3/s.

9. In discharge of water over narrow crested weir, discharge is directly proportional to the second power of height.
a) True
b) False
Answer: b
Examples: In discharge of water over narrow crested weir, discharge is directly proportional to the one and half power of height.

10. In discharge of water over Ogee weir, discharge is directly proportional to the first power of length.
a) True
b) False
Answer: a
Clarification: This is as per empirical relation.

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250+ TOP MCQs on Effect of Acceleration in Suction and Delivery Pipes on Indicator Diagrams and Answers

Fluid Mechanics Multiple Choice Questions on “Effect of Acceleration in Suction and Delivery Pipes on Indicator Diagrams”.

1. What is the full form of NPSH?
a) Net pipe suction head
b) Net positive suction head
c) Non-positive suction head
d) Non-polar suction head
Answer: b
Clarification: The full form of NPSH is net positive suction head. It is defined as the margin of pressure over vapour pressure. It happens at the pump suction nozzle.

2. What is the formula for NPSH?
a) Ps-Pvap
b) Vs-Vvap
c) Ts-Tvap
d) Ms-Mvap
Answer: a
Clarification: NPSH is defined as the margin of pressure over vapour pressure. It happens at the pump suction nozzle. It is the difference between the suction pressure and vapour pressure. Thus, the correct option is Ps-Pvap.

3. What is absolute pressure?
a) Momentum pressure to thermal pressure
b) Thermal pressure to momentum pressure
c) Atmospheric pressure plus gauge pressure
d) Atmospheric pressure by gauge pressure
Answer: c
Clarification: Absolute pressure is defined as the summation of Atmospheric pressure plus gauge pressure. This equation provides the answer in units of pressure. The obtained psi can be converted to units of head.

4. What is the unit of NPSH?
a) kPa
b) kgm
c) kg/m
d) kg
Answer: a
Clarification: Unit of NPSH can be expressed as units of specific energies. All the units in NPSH are psi units. The psi units are kilopascal, bar, pounds per square inch etc. So, kPa is the correct option.

5. What does ‘g’ in psig mean?
a) Pressure is measured below absolute pressure
b) Pressure is measured above absolute pressure
c) Pressure is measured below absolute zero
d) Pressure is measured above absolute zero
Answer: b
Clarification: All the units in NPSH are psi units. The psi units are kilopascal, bar, pounds per square inch etc. The ‘g’ in psig indicates that the pressure is measured above the absolute pressure.

6. What does ‘a’ in psia mean?
a) Pressure is measured below absolute pressure
b) Pressure is measured above absolute pressure
c) Pressure is measured below absolute zero
d) Pressure is measured above absolute zero
Answer: d
Clarification: All the units in NPSH are psi units. The psi units are kilopascal, bar, pounds per square inch etc. The ‘a’ in psia indicates that the pressure is measured above absolute zero which is a perfect vacuum.

7. Which among the following happens at the first half of NPSH?
a) Vapour pressure
b) Atmospheric pressure
c) Suction pressure
d) Discharge pressure
Answer: c
Clarification: During the first half of the NPSH, the suction of air takes place. For the suction of an air, a strong suction pressure is required. Sometimes, the elevation of gauge must also be added. But, most of the times it is considered negligible.

8. Which among the following happens in the second half of NPSH?
a) Vapour pressure
b) Atmospheric pressure
c) Suction pressure
d) Discharge pressure
Answer: a
Clarification: During the second half of the NPSH, vapour pressure is more difficult to determine. It is a measure of the desire of liquids. Cool water has a low vapour pressure. Thus, the option is Vapour pressure.

9. Vapour pressure depends on_______
a) Pressure
b) Temperature
c) Density
d) Viscosity
Answer: b
Clarification: Vapour pressure depends on temperature only. With the increase in temperature, the vapour pressure increases. It increases until it reaches the critical temperature. At the critical temperature, the vapour pressure tends to slowly vanish.

10. Which among the following is not a type of pipe?
a) Stainless steel pipes
b) PVC piping
c) Brass pipes
d) Wooden pipes
Answer: d
Clarification: Wooden pipes for transportation and other important facilities is not feasible. Wood has various properties against water. Water flowing through the wooden pipe will slowly reduce the strength of the wood which may lead to cracks.

250+ TOP MCQs on Stagnation Properties and Answers

Fluid Mechanics Multiple Choice Questions on “Stagnation Properties”.

1. __________ is referred as the temperature at a stagnation point in the flow of fluids in fluid mechanics and thermodynamics.
a) Absolute temperature
b) Maximum temperature
c) Stagnation temperature
d) Hydraulic temperature

Answer: c
Clarification: Stagnation temperature is the temperature at the stagnation point of the flow of fluids. In thermodynamics and fluid mechanics, these terms find application. At a stagnation point the speed of the fluid is zero and all of the kinetic energy has been converted to internal energy and is added to the local static enthalpy.

2. In ________ and _______ kind of flow, the stagnation temperature is equal to the total temperature
a) compressible, incompressible
b) stagnated, non-stagnated
c) dynamic, non-dynamic
d) turbulent, passive

Answer: a
Clarification: In compressible and incompressible kind of flow, the stagnation temperature is equal to the total temperature. This occurs at all points on the streamline. Eventually, this leads to the stagnation point.

3. _____ is the law employed in the derivation of stagnation point.
a) Hooke’s law
b) Poisson’s law
c) Second law of thermodynamics
d) First law of thermodynamics

Answer: d
Clarification: First law of thermodynamics is the law employed in the derivation of stagnation point. It states that the change in the internal energy ΔU of a closed system is equal to the amount of heat Q supplied to the system, subtracting the amount of work W done by the system on its surroundings. It is a modified form of the law of conservation of energy.

4. A bimetallic ________ is generally utilized to measure stagnation temperature
a) Transistor
b) Thermometer
c) Diode
d) Thermocouple

Answer: d
Clarification: A bimetallic thermocouple is generally utilized to measure stagnation temperature. However, there must be allowances for thermal radiation. This is done in order to avoid the occurrence of errors.

5. Stagnation point is the point in fluid mechanics where the velocity of the fluid at that point is _____
a) zero
b) infinite
c) constant
d) unity

Answer: a
Clarification: Stagnation point is the point in fluid mechanics where the velocity of the fluid at that point is zero. Stagnation points occur at places where the fluid is brought to a state of rest by an object. They usually exist at the surface of objects.

6. _________ proves that the static pressure is maximum when the velocity is zero
a) Laws of Thermodynamics
b) Bernoulli’s Equation
c) Hooke’s law
d) Principle of continuity

Answer: b
Clarification: Bernoulli’s equation proves that the static pressure is maximum when the velocity is zero. Bernoulli’s principle states that a rise in the speed of a fluid occurs simultaneously with a drop in pressure or a drop in the fluid’s potential energy. It is named after Daniel Bernoulli, who stated it.

7. Total pressure is an addition of static pressure and ______
a) Dynamic pressure
b) Stagnation pressure
c) Fluid pressure
d) Instantaneous pressure

Answer: a
Clarification: Total pressure is an addition of static pressure and dynamic pressure. In incompressible flow, the stagnation pressure is equal to the sum of dynamic pressure and static pressure. So here, stagnation pressure is equal to total pressure.

8. The pressure coefficient at a stagnation point is _____
a) +1
b) -1
c) 0
d) Infinite

Answer: a
Clarification: The pressure coefficient at a stagnation point is unity. This is referred to as +1. A pressure coefficient is a dimensionless number which describes the relative pressures throughout a flow field in fluid dynamics.

9. _________ minus freestream static pressure gives freestream dynamic pressure
a) Stagnation pressure
b) Total pressure
c) Fluid pressure
d) Instantaneous pressure

Answer: a
Clarification: Stagnation pressure minus freestream static pressure gives freestream dynamic pressure. This plays an important role in determining the pressure coefficient. Hence, the pressure coefficient at stagnation points is +1.

10. On a streamlined body fully immersed in a potential flow, there are ____ stagnation points
a) 1
b) 2
c) 0
d) Infinite

Answer: b
Clarification: On a streamlined body fully immersed in a potential flow, there are 2 stagnation points. One point is present near the leading edge. The other point is present near the trailing edge.

250+ TOP MCQs on Fluid Pressure at a Point and Pascal’s Law and Answers

Fluid Mechanics Interview Questions and Answers for Experienced people on “Fluid Pressure at a Point & Pascal’s Law”.

1. A Hydraulic press has a ram of 30 cm diameter and a plunger of of 2 cm diameter. It is used for lifting a weight of 35 kN. Find the force required at the plunger.
a) 233.3 kN
b) 311.1 kN
c) 466.6 kN
d) 155.5 kN
Answer: d
Clarification: F/a=W/A
F=(35000*3.142*.02*.02)/(3.142*0.3*0.3)
=155.5 kN.

2. The pressure at a point in the fluid is 4.9 N/cm2. Find height when the fluid under consideration is in oil of specific gravity of 0.85.
a) 5.83 m
b) 11.66 m
c) 17.49 m
d) 8.74 m
Answer: a
Clarification: Height=p/ρg
=48620/850*9.81
=5.83 m.

3. An open tank contains water upto a depth of 350 cm and above it an oil of specific gravity 0.65 for a depth of 2.5 m. Find the pressure intensity at the extreme bottom of the tank.
a) 5.027 N/cm2
b) 10.05 N/cm2
c) 2.51 N/cm2
d) None of the mentioned
Answer: a
Clarification: p= (specific gravity of water* height of water + specific gravity of oil* height of oil) * 9.81
= 5.027 N/cm2.

4. The diameters of a small piston and a large piston of a hydraulic jack are 45 mm and 100 mm respectively.Force of 0.09 kN applied on smaller in size piston. Find load lifted by piston if smaller in size piston is 40 cm above the large piston. The density of fluid is 850 kg/m3
a) 60 N/cm2
b) 12 N/cm2
c) 30 N/cm2
d) None of the mentioned
Answer: a
Clarification: Pressure at bottom of tank =ρgh + F/a
=850*9.81*0.4 + 90/3.142*0.045*0.045
=60 N/cm2.

5. If fluid is at rest in a container of a narrow mouth at a certain column height and same fluid is at rest at same column height in a container having broad mouth, will the pressure be different at certain depth from fluid surface.
a) Pressure will be same for both.
b) Pressure will be more for narrower mouth
c) Pressure will be less for narrower mouth
d) None of the mentioned
Answer: a
Clarification: As per hydrostatic law, the pressure depends only on the height of water column and not its shape.

6. We can draw Mohr’s circle for a fluid at rest.
a) True
b) false
Answer: b
Clarification: Mohr’s circle is used to denote shear stress distribution. For fluid at rest, there is no shear stress. Hence, we cannot draw Mohr’s circle for fluid at rest.

7. Pressure intensity or force due to pressure gradient for fluid at rest is considered as which kind of force?
a) Surface force
b) Body force
c) Force due to motion
d) None of the mentioned
Answer: a
Clarification: Pressure force is surface force.

8. Calculate the hydrostatic pressure for water moving with constant velocity at a depth of 5 m from the surface.
a) 49 kN/m2
b) 98 kN/m2
c) since fluid is in motion, we cannot analyse
d) None of the mentioned
Answer: a
Clarification: If fluid is moving with uniform velocity we treat it analytically same as if fluid is at rest
p= ρgh.

9. Pressure distribution for fluid at rest takes into consideration pressure due to viscous force.
a) True
b) False
Answer: b
Clarification: Viscous force term in pressure expression for fluid at rest is absent as their is no motion of liquid.

10. Barometer uses the principle of fluid at rest or pressure gradient for its pressure calculation.
a) True
b) False
Answer: a
Clarification: Principle of Barometer is Hydrostatic law.

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250+ TOP MCQs on Velocity and Acceleration and Answers

Fluid Mechanics Multiple Choice Questions on “Velocity and Acceleration”.

1. The velocity vector in a fluid is given V=5x4+3y2+2z( in metre/sec). What is the acceleration of it at point (1,3,4) ?
a) 40 m/s2
b) 20 m/s2
c) 60 m/s2
d) 80 m/s2
Answer: a
Clarification: By differentiating V=5x4+3y2+2z, the acceleration obtained is V=20x3+6y+2.
on putting the coordinates, the acceleration obtained is 40 m/s2.

2. Determine the third velocity component such that continuity equation is satisfied if two components are u=2y2, w=2xyz.
a) -2xy+x2y+f(y,z)
b) 4xy-x2y+f(y,z)
c) -4xy-x2y+f(y,z)
d) -2xy-x2y+f(y,z)
Answer: c
Clarification: The continuity equation for incompressible is du/dx+dv/dy+dw/dz = 0.
Here du/dx=0 and w=2xy.
On solving by integrating, we get v = -4xy-x2y+f(y,z).

3. Determine the third velocity component such that continuity equation is satisfied if two components are u=x2+y2+z2, v=xy2 – yz2 + xy
a) -3xz-2xyz+z2/3+f(y,z)
b) -3xz+2xyz+z3/3+f(y,z)
c) -3xz-2xyz+z3/3+f(x,z)
d) -3xz-2xyz+z3/3+f(y,z)
Answer: d
Clarification: The continuity equation for incompressible is du/dx+dv/dy+dw/dz = 0.
Here du/dx=2x and v=2xy-z2
On solving by integrating, we get w = -3xz-2xyz+z3/3+f(y,z),

4. A fluid flow field is given by
V=x2yi+y2z-(2xyz+yz)k
Calculate it’s acceleration at the point (1,3,5)
a) 28i-3j+125k
b) 28i-3j-125k
c) 28i+3j+125k
d) None of the mentioned
Answer: d
Clarification: First we have to check whether it satisfies the continuity equation,
The continuity equation for incompressible is du/dx+dv/dy+dw/dz = 0.
(here d/dx, d/dy, d/z represent partial derivative)
The given equation doesn’t satisfy the continuity equation.

5. A fluid flow field is given by
V=y2xi+z2x-(2xyz+yz)k
Calculate it’s acceleration at the point (2,4,4)
a) 36i-27j+100k
b) 36i-27j-100k
c) 28i+27j+100k
d) 36ne of the mentioned
Answer: d
Clarification: First we have to check whether it satisfies the continuity equation,
The continuity equation for incompressible is du/dx+dv/dy+dw/dz = 0.
(here d/dx, d/dy, d/z represent partial derivative)
The given equation doesn’t satisfy the continuity equation.

6. Convective acceleration cannot be found if the fluid flow equation is not satisfying
the continuity equation but local acceleration can be found.
a) True
b) False
Answer: b
Clarification: Convective acceleration and local acceleration cannot be found if the fluid flow equation is not satisfying the continuity equation.

7. Local acceleration has constant value for a steady flow.
a) True
b) False
Answer: b
Clarification: Local acceleration is zero for a steady flow.

8. Total acceleration has the same value as convective acceleration in case of unsteady flow.
a) True
b) False
Answer: b
Clarification: Total acceleration has the same value as convective acceleration in case of steady flow as local acceleration value becomes zero.

9. Which equation must be perfunctorily satisfied while dealing with fluid flow problems?
a) Newton’s second law
b) Newton’s third law
c) Law of conservation of momentum
d) Continuity equation
Answer: d
Clarification: Continuity equation must be perfunctorily satisfied while dealing with fluid flow problems.

10. Convective acceleration is defined as the rate of change of velocity due to change of velocity with respect to time.
a) True
b) False
Answer: b
Clarification: Convective acceleration is defined as the rate of change of velocity due to change of position of fluid particles.