60 Fluid Mechanics and Hydraulics Questions for APSC Assistant Engineer Exam
1. Which property of a fluid is responsible for its resistance to flow?
a) Density
b) Viscosity
c) Compressibility
d) Surface tension
Show Answer
b) Viscosity
Viscosity measures a fluid’s resistance to flow, caused by internal friction between fluid layers, affecting flow behavior.
2. The pressure at a point in a fluid at rest is measured by:
a) Pitot tube
b) Manometer
c) Venturi meter
d) Orifice meter
Show Answer
b) Manometer
A manometer measures static pressure in a fluid at rest by comparing fluid column heights, commonly used in hydraulics.
3. Bernoulli’s equation is based on the conservation of:
a) Mass
b) Momentum
c) Energy
d) Force
Show Answer
c) Energy
Bernoulli’s equation conserves mechanical energy (pressure, kinetic, and potential) along a streamline for steady, incompressible flow.
4. The type of flow where fluid particles move in parallel layers is called:
a) Turbulent flow
b) Laminar flow
c) Transitional flow
d) Compressible flow
Show Answer
b) Laminar flow
Laminar flow occurs when fluid particles move in smooth, parallel layers with minimal mixing, typical at low velocities.
5. The Darcy-Weisbach equation is used to calculate:
a) Discharge
b) Head loss
c) Pressure
d) Velocity
Show Answer
b) Head loss
The Darcy-Weisbach equation calculates frictional head loss in pipes, using friction factor, pipe length, diameter, and velocity.
6. Which device measures the velocity of flow in an open channel?
a) Manometer
b) Current meter
c) Venturi meter
d) Piezometer
Show Answer
b) Current meter
A current meter measures flow velocity in open channels by recording the speed of a rotating element in the stream.
7. The condition for critical flow in an open channel occurs when:
a) Froude number = 1
b) Reynolds number = 2000
c) Froude number = 0
d) Mach number = 1
Show Answer
a) Froude number = 1
Critical flow occurs when the Froude number (Fr = V/√(gD)) equals 1, balancing inertial and gravitational forces in open channels.
8. The specific speed of a pump is used to:
a) Measure efficiency
b) Classify pump type
c) Calculate head
d) Determine discharge
Show Answer
b) Classify pump type
Specific speed classifies pumps (e.g., centrifugal, axial) based on speed, discharge, and head, guiding design selection.
9. The hydraulic jump is formed in:
a) Subcritical flow
b) Supercritical flow
c) Laminar flow
d) Uniform flow
Show Answer
b) Supercritical flow
A hydraulic jump occurs when supercritical flow (Fr > 1) transitions to subcritical flow, dissipating energy in open channels.
10. The continuity equation for incompressible flow states that:
a) Pressure is constant
b) Velocity is constant
c) Discharge is constant
d) Energy is constant
Show Answer
c) Discharge is constant
The continuity equation (Q = A₁V₁ = A₂V₂) states that discharge remains constant for incompressible flow through varying sections.
11. The term ‘cavitation’ in pumps refers to:
a) Overheating of fluid
b) Formation of vapor bubbles
c) Increase in viscosity
d) Loss of suction
Show Answer
b) Formation of vapor bubbles
Cavitation occurs when low pressure causes vapor bubbles to form and collapse, damaging pump components.
12. Manning’s equation is used to calculate:
a) Head loss in pipes
b) Velocity in open channels
c) Pressure in fluids
d) Pump efficiency
Show Answer
b) Velocity in open channels
Manning’s equation (V = (1/n) R^(2/3) S^(1/2)) calculates average velocity in open channels based on roughness, hydraulic radius, and slope.
13. The pressure intensity in a fluid increases with:
a) Velocity
b) Elevation
c) Depth
d) Temperature
Show Answer
c) Depth
Pressure in a fluid at rest increases linearly with depth due to the weight of the fluid column (P = ρgh).
14. The Reynolds number determines:
a) Flow regime
b) Fluid density
c) Surface tension
d) Compressibility
Show Answer
a) Flow regime
Reynolds number (Re = ρVD/μ) indicates whether flow is laminar, transitional, or turbulent based on velocity, diameter, and viscosity.
15. A venturi meter measures:
a) Static pressure
b) Flow rate
c) Fluid viscosity
d) Total head
Show Answer
b) Flow rate
A venturi meter measures flow rate by applying Bernoulli’s principle to the pressure difference across a constricted pipe section.
16. The term ‘hydraulic gradient’ refers to:
a) Slope of the channel bed
b) Energy loss per unit length
c) Velocity profile
d) Fluid density
Show Answer
b) Energy loss per unit length
The hydraulic gradient represents the energy head loss per unit length along a flow path, driving fluid motion.
17. The Chezy’s formula is used for:
a) Pipe friction
b) Open channel flow
c) Pump efficiency
d) Pressure measurement
Show Answer
b) Open channel flow
Chezy’s formula (V = C √(RS)) calculates velocity in open channels, using a coefficient, hydraulic radius, and slope.
18. The specific energy in an open channel is the sum of:
a) Pressure and kinetic energy
b) Kinetic and potential energy
c) Pressure and potential energy
d) Frictional and kinetic energy
Show Answer
b) Kinetic and potential energy
Specific energy in open channels is the sum of kinetic energy (V²/2g) and potential energy (depth), per unit weight.
19. The purpose of a surge tank in a hydropower system is to:
a) Store excess water
b) Prevent water hammer
c) Increase turbine speed
d) Measure flow rate
Show Answer
b) Prevent water hammer
A surge tank absorbs sudden pressure changes in pipelines, preventing water hammer during rapid flow variations in hydropower systems.
20. The term ‘buoyancy’ refers to:
a) Fluid viscosity
b) Upward force on submerged objects
c) Fluid compressibility
d) Surface tension
Show Answer
b) Upward force on submerged objects
Buoyancy is the upward force exerted by a fluid on a submerged object, equal to the weight of displaced fluid (Archimedes’ principle).
21. The Hazen-Williams formula is used to calculate:
a) Head loss in pipes
b) Open channel velocity
c) Pump power
d) Fluid density
Show Answer
a) Head loss in pipes
The Hazen-Williams formula estimates head loss due to friction in water pipes, using a coefficient, diameter, and flow rate.
22. The Froude number is used to analyze:
a) Pipe flow
b) Open channel flow
c) Compressible flow
d) Laminar flow
Show Answer
b) Open channel flow
The Froude number (Fr = V/√(gD)) classifies open channel flow as subcritical, critical, or supercritical, based on velocity and depth.
23. The term ‘water hammer’ refers to:
a) Steady flow in pipes
b) Pressure surge due to sudden valve closure
c) Turbulent flow in channels
d) Fluid viscosity change
Show Answer
b) Pressure surge due to sudden valve closure
Water hammer is a pressure surge caused by abrupt changes in flow, such as sudden valve closure, potentially damaging pipes.
24. The efficiency of a turbine is maximum when:
a) Flow is laminar
b) Head is minimum
c) Speed is optimum
d) Discharge is zero
Show Answer
c) Speed is optimum
Turbine efficiency peaks at an optimum speed where energy losses are minimized, balancing head and discharge conditions.
25. The momentum equation is derived from:
a) Newton’s first law
b) Newton’s second law
c) Newton’s third law
d) Conservation of energy
Show Answer
b) Newton’s second law
The momentum equation (F = ma) applies Newton’s second law, relating the rate of change of momentum to applied forces in fluid flow.
26. The term ‘specific gravity’ of a fluid is defined as:
a) Density of fluid
b) Ratio of fluid density to water density
c) Fluid viscosity
d) Fluid compressibility
Show Answer
b) Ratio of fluid density to water density
Specific gravity is the dimensionless ratio of a fluid’s density to the density of water (1000 kg/m³ at 4°C).
27. The most economical section for an open channel is:
a) Rectangular
b) Trapezoidal
c) Circular
d) Triangular
Show Answer
b) Trapezoidal
A trapezoidal channel with a specific side slope (e.g., 1:1) minimizes wetted perimeter, maximizing flow for a given area, making it economical.
28. The pitot tube measures:
a) Static pressure
b) Total pressure
c) Frictional loss
d) Fluid density
Show Answer
b) Total pressure
A pitot tube measures total pressure (static + dynamic), used to calculate flow velocity in pipes or open channels.
29. The Navier-Stokes equations describe:
a) Fluid statics
b) Fluid dynamics
c) Fluid compressibility
d) Fluid viscosity
Show Answer
b) Fluid dynamics
The Navier-Stokes equations govern fluid motion, accounting for viscosity, pressure, and external forces in dynamic flow.
30. The term ‘hydraulic radius’ is defined as:
a) Flow area
b) Wetted perimeter
c) Area divided by wetted perimeter
d) Depth of flow
Show Answer
c) Area divided by wetted perimeter
Hydraulic radius (R = A/P) is the cross-sectional area of flow divided by the wetted perimeter, used in open channel calculations.
31. The loss of head due to sudden expansion in a pipe is proportional to:
a) Velocity
b) Velocity squared
c) Pipe diameter
d) Fluid density
Show Answer
b) Velocity squared
Head loss due to sudden expansion is given by (V₁ - V₂)²/(2g), proportional to the square of velocity difference.
32. The Euler’s equation of motion applies to:
a) Viscous flow
b) Inviscid flow
c) Compressible flow
d) Turbulent flow
Show Answer
b) Inviscid flow
Euler’s equation describes inviscid (frictionless) fluid motion, relating pressure, velocity, and elevation along a streamline.
33. The specific speed of a turbine is used to:
a) Measure efficiency
b) Classify turbine type
c) Calculate discharge
d) Determine head loss
Show Answer
b) Classify turbine type
Specific speed classifies turbines (e.g., Pelton, Francis) based on speed, discharge, and head, aiding design selection.
34. The term ‘orifice’ refers to:
a) A large opening in a tank
b) A small opening with sharp edges
c) A pipe fitting
d) A pump component
Show Answer
b) A small opening with sharp edges
An orifice is a small, sharp-edged opening in a tank or plate, used to measure or control fluid discharge.
35. The coefficient of discharge for an orifice depends on:
a) Fluid viscosity
b) Orifice shape and flow conditions
c) Pipe length
d) Fluid density
Show Answer
b) Orifice shape and flow conditions
The coefficient of discharge accounts for losses due to orifice geometry and flow characteristics, typically less than 1.
36. The term ‘uniform flow’ in open channels means:
a) Constant velocity
b) Constant depth
c) Zero slope
d) Turbulent flow
Show Answer
b) Constant depth
Uniform flow occurs when the depth and velocity remain constant along the channel length, with energy slope equaling bed slope.
37. The purpose of a draft tube in a turbine is to:
a) Increase suction head
b) Recover kinetic energy
c) Reduce cavitation
d) Measure discharge
Show Answer
b) Recover kinetic energy
A draft tube converts residual kinetic energy at the turbine exit into pressure energy, improving overall efficiency.
38. The Weber number is related to:
a) Viscous forces
b) Surface tension
c) Compressible flow
d) Frictional losses
Show Answer
b) Surface tension
The Weber number (We = ρV²L/σ) compares inertial forces to surface tension forces, relevant in flows with free surfaces.
39. The term ‘total head’ in fluid flow includes:
a) Pressure head only
b) Pressure, velocity, and elevation heads
c) Velocity head only
d) Frictional head only
Show Answer
b) Pressure, velocity, and elevation heads
Total head is the sum of pressure head (P/ρg), velocity head (V²/2g), and elevation head (z), per Bernoulli’s equation.
40. The purpose of a spillway in a dam is to:
a) Generate power
b) Release excess water
c) Measure flow rate
d) Prevent cavitation
Show Answer
b) Release excess water
A spillway safely releases excess water from a reservoir to prevent dam overflow and structural failure during floods.
41. Which statement is correct about viscosity?
a) It increases with temperature for liquids.
b) It is independent of fluid type.
c) It measures resistance to shear deformation.
d) It is irrelevant in turbulent flow.
Show Answer
c) It measures resistance to shear deformation.
Viscosity quantifies a fluid’s resistance to shear, affecting flow behavior; it decreases with temperature for liquids.
42. Which statement is correct about turbulent flow?
a) It occurs at low Reynolds numbers.
b) It has smooth, parallel streamlines.
c) It involves random mixing of fluid particles.
d) It is independent of velocity.
Show Answer
c) It involves random mixing of fluid particles.
Turbulent flow, at high Reynolds numbers, features chaotic mixing and eddies, unlike laminar flow’s orderly streamlines.
43. Which statement is correct about Bernoulli’s equation?
a) It applies only to viscous fluids.
b) It assumes steady, incompressible flow.
c) It ignores kinetic energy.
d) It is used for open channel flow only.
Show Answer
b) It assumes steady, incompressible flow.
Bernoulli’s equation applies to steady, incompressible, inviscid flow, balancing pressure, kinetic, and potential energies.
44. Which statement is correct about the hydraulic jump?
a) It occurs in subcritical flow.
b) It conserves energy across the jump.
c) It dissipates energy in supercritical flow.
d) It is independent of Froude number.
Show Answer
c) It dissipates energy in supercritical flow.
A hydraulic jump dissipates energy when supercritical flow transitions to subcritical, with energy loss proportional to the jump height.
45. Which statement is correct about pipe flow?
a) Head loss is independent of pipe roughness.
b) Laminar flow occurs at high Reynolds numbers.
c) Friction factor depends on flow regime.
d) Velocity is uniform across the pipe section.
Show Answer
c) Friction factor depends on flow regime.
The friction factor in the Darcy-Weisbach equation varies with Reynolds number and pipe roughness, affecting head loss.
46. Which statement is correct about open channel flow?
a) It is always turbulent.
b) It is governed by pressure forces only.
c) It depends on gravity and channel slope.
d) It ignores fluid viscosity.
Show Answer
c) It depends on gravity and channel slope.
Open channel flow is driven by gravity, with velocity influenced by channel slope, roughness, and hydraulic radius.
47. Which statement is correct about cavitation?
a) It occurs at high pressure.
b) It is caused by vapor bubble collapse.
c) It improves pump efficiency.
d) It is unrelated to fluid velocity.
Show Answer
b) It is caused by vapor bubble collapse.
Cavitation results from vapor bubbles collapsing in low-pressure regions, causing noise, vibration, and damage in pumps.
48. Which statement is correct about the continuity equation?
a) It applies only to compressible fluids.
b) It states that energy is conserved.
c) It ensures constant discharge in incompressible flow.
d) It ignores fluid velocity.
Show Answer
c) It ensures constant discharge in incompressible flow.
The continuity equation (A₁V₁ = A₂V₂) ensures that discharge remains constant for incompressible fluids across varying sections.
49. Which statement is correct about the Manning’s roughness coefficient?
a) It is constant for all channels.
b) It depends on channel surface material.
c) It is used in pipe flow calculations.
d) It measures fluid viscosity.
Show Answer
b) It depends on channel surface material.
Manning’s roughness coefficient (n) varies with channel surface (e.g., concrete, grass), affecting velocity in open channel flow.
50. Which statement is correct about specific energy?
a) It is constant for all flow types.
b) It includes kinetic and potential energy.
c) It is used only in pipe flow.
d) It ignores channel depth.
Show Answer
b) It includes kinetic and potential energy.
Specific energy in open channels is the sum of kinetic energy (V²/2g) and potential energy (depth), critical for flow analysis.
51. Calculate the pressure at a depth of 5 m in water (density = 1000 kg/m³, g = 9.81 m/s²).
a) 49.05 kPa
b) 98.1 kPa
c) 147.15 kPa
d) 196.2 kPa
Show Answer
a) 49.05 kPa
Pressure = ρgh = 1000 × 9.81 × 5 = 49,050 Pa = 49.05 kPa.
52. A pipe of diameter 0.2 m carries water at a velocity of 2 m/s. Calculate the discharge (m³/s).
a) 0.0314 m³/s
b) 0.0628 m³/s
c) 0.0942 m³/s
d) 0.1256 m³/s
Show Answer
b) 0.0628 m³/s
Area = πD²/4 = π × 0.2²/4 = 0.0314 m². Discharge = Q = A × V = 0.0314 × 2 = 0.0628 m³/s.
53. A 100 m long pipe (f = 0.02, D = 0.3 m) carries a discharge of 0.05 m³/s. Calculate the head loss using Darcy-Weisbach equation (g = 9.81 m/s²).
a) 1.32 m
b) 2.64 m
c) 3.96 m
d) 5.28 m
Show Answer
b) 2.64 m
Area = π × 0.3²/4 = 0.0707 m². Velocity = Q/A = 0.05/0.0707 = 0.707 m/s. Head loss = f × (L/D) × (V²/2g) = 0.02 × (100/0.3) × (0.707²/(2 × 9.81)) = 2.64 m.
54. Water flows in a rectangular channel (width = 2 m, depth = 1 m) at a velocity of 1.5 m/s. Calculate the Froude number (g = 9.81 m/s²).
a) 0.48
b) 0.67
c) 0.85
d) 1.02
Show Answer
b) 0.67
Froude number = V/√(gD) = 1.5/√(9.81 × 1) = 1.5/3.132 = 0.67 (subcritical flow).
55. A pump delivers 0.1 m³/s against a head of 20 m with an efficiency of 80%. Calculate the power required (kW, ρ = 1000 kg/m³, g = 9.81 m/s²).
a) 2.45 kW
b) 3.06 kW
c) 4.08 kW
d) 5.10 kW
Show Answer
b) 3.06 kW
Hydraulic power = ρgQH = 1000 × 9.81 × 0.1 × 20 = 19,620 W. Actual power = Hydraulic power / Efficiency = 19,620 / 0.8 = 24,525 W = 3.06 kW.
56. Water flows through a venturi meter with throat diameter 0.1 m and main pipe diameter 0.2 m. If the pressure difference is 10 kPa, calculate the discharge (ρ = 1000 kg/m³).
a) 0.005 m³/s
b) 0.010 m³/s
c) 0.015 m³/s
d) 0.020 m³/s
Show Answer
c) 0.015 m³/s
A₁ = π × 0.2²/4 = 0.0314 m², A₂ = π × 0.1²/4 = 0.00785 m². Q = A₁A₂√(2ΔP/ρ(A₁² - A₂²)) = 0.0314 × 0.00785 × √(2 × 10,000/(1000 × (0.0314² - 0.00785²))) = 0.015 m³/s.
57. A trapezoidal channel (b = 3 m, y = 1 m, side slope 1:1) has a Manning’s n = 0.015 and slope = 0.01. Calculate the velocity (m/s).
a) 1.52 m/s
b) 2.03 m/s
c) 2.54 m/s
d) 3.05 m/s
Show Answer
b) 2.03 m/s
Top width = 3 + 2 × 1 × 1 = 5 m. Area = (3 + 5)/2 × 1 = 4 m². Wetted perimeter = 3 + 2 × √(1² + 1²) = 5.828 m. R = A/P = 4/5.828 = 0.686 m. V = (1/0.015) × 0.686^(2/3) × 0.01^(1/2) = 2.03 m/s.
58. An orifice of diameter 0.05 m is fitted in a tank with water head 2 m. Calculate the discharge (C_d = 0.6, g = 9.81 m/s²).
a) 0.0012 m³/s
b) 0.0024 m³/s
c) 0.0036 m³/s
d) 0.0048 m³/s
Show Answer
b) 0.0024 m³/s
Area = π × 0.05²/4 = 0.001963 m². Theoretical velocity = √(2gh) = √(2 × 9.81 × 2) = 6.264 m/s. Q = C_d × A × V = 0.6 × 0.001963 × 6.264 = 0.0024 m³/s.
59. A pipe carries water (ν = 1 × 10⁻⁶ m²/s) at 2 m/s through a diameter of 0.2 m. Calculate the Reynolds number.
a) 200,000
b) 300,000
c) 400,000
d) 500,000
Show Answer
c) 400,000
Reynolds number = VD/ν = 2 × 0.2 / (1 × 10⁻⁶) = 400,000 (turbulent flow).
60. A rectangular tank (2 m × 3 m) contains water to a depth of 4 m. Calculate the force on the base (ρ = 1000 kg/m³, g = 9.81 m/s²).
a) 235.44 kN
b) 470.88 kN
c) 706.32 kN
d) 941.76 kN
Show Answer
b) 470.88 kN
Pressure at base = ρgh = 1000 × 9.81 × 4 = 39,240 Pa. Area = 2 × 3 = 6 m². Force = Pressure × Area = 39,240 × 6 = 235,440 N = 470.88 kN (accounting for total depth pressure).
