APSC AE Mechanical Exam - Fluid Mechanics & Hydraulic Machines MCQs
1. What is the SI unit of viscosity?
Answer: b) N·s/m²
Description: Viscosity measures a fluid's resistance to flow. Dynamic viscosity in SI units is expressed as N·s/m² (or Pa·s), which represents the force per unit area required to maintain a unit velocity gradient. Kinematic viscosity uses m²/s.
Description: Viscosity measures a fluid's resistance to flow. Dynamic viscosity in SI units is expressed as N·s/m² (or Pa·s), which represents the force per unit area required to maintain a unit velocity gradient. Kinematic viscosity uses m²/s.
2. A fluid has a density of 1000 kg/m³ and a viscosity of 0.001 N·s/m². What is its kinematic viscosity?
Answer: a) 10⁻³ m²/s
Description: Kinematic viscosity (ν) is dynamic viscosity (μ) divided by density (ρ). Given μ = 0.001 N·s/m² and ρ = 1000 kg/m³, ν = μ/ρ = 0.001/1000 = 10⁻³ m²/s.
Description: Kinematic viscosity (ν) is dynamic viscosity (μ) divided by density (ρ). Given μ = 0.001 N·s/m² and ρ = 1000 kg/m³, ν = μ/ρ = 0.001/1000 = 10⁻³ m²/s.
3. Which of the following statements is true about Bernoulli’s equation?
Answer: b) It assumes steady, incompressible, and inviscid flow
Description: Bernoulli’s equation relates pressure, velocity, and elevation in a fluid flow, assuming steady, incompressible, and inviscid (no viscosity) conditions. It conserves total energy along a streamline.
Description: Bernoulli’s equation relates pressure, velocity, and elevation in a fluid flow, assuming steady, incompressible, and inviscid (no viscosity) conditions. It conserves total energy along a streamline.
4. Calculate the pressure at a depth of 10 m in water (density = 1000 kg/m³, g = 9.81 m/s²).
Answer: a) 98.1 kPa
Description: Hydrostatic pressure is given by P = ρgh. Substituting ρ = 1000 kg/m³, g = 9.81 m/s², and h = 10 m, P = 1000 × 9.81 × 10 = 98100 Pa = 98.1 kPa.
Description: Hydrostatic pressure is given by P = ρgh. Substituting ρ = 1000 kg/m³, g = 9.81 m/s², and h = 10 m, P = 1000 × 9.81 × 10 = 98100 Pa = 98.1 kPa.
5. In a hydraulic press, the force applied to a small piston of area 0.01 m² is 100 N. If the large piston has an area of 0.1 m², what is the force on the large piston?
Answer: b) 1000 N
Description: By Pascal’s principle, pressure is transmitted equally. Pressure P = F₁/A₁ = 100/0.01 = 10000 Pa. Force on the large piston F₂ = P × A₂ = 10000 × 0.1 = 1000 N.
Description: By Pascal’s principle, pressure is transmitted equally. Pressure P = F₁/A₁ = 100/0.01 = 10000 Pa. Force on the large piston F₂ = P × A₂ = 10000 × 0.1 = 1000 N.
6. Which of the following is a dimensionless number?
Answer: b) Reynolds number
Description: Reynolds number (Re = ρvD/μ) is a dimensionless quantity used to predict flow patterns (laminar or turbulent). Viscosity, pressure, and density have dimensions.
Description: Reynolds number (Re = ρvD/μ) is a dimensionless quantity used to predict flow patterns (laminar or turbulent). Viscosity, pressure, and density have dimensions.
7. The continuity equation is based on the principle of:
Answer: b) Conservation of mass
Description: The continuity equation (A₁v₁ = A₂v₂ for incompressible fluids) ensures that the mass flow rate remains constant in a flow system, reflecting conservation of mass.
Description: The continuity equation (A₁v₁ = A₂v₂ for incompressible fluids) ensures that the mass flow rate remains constant in a flow system, reflecting conservation of mass.
8. A pipe has a diameter of 0.2 m and water flows at a velocity of 2 m/s. What is the discharge rate?
Answer: a) 0.0628 m³/s
Description: Discharge Q = A × v. Area A = πr² = π(0.1)² = 0.0314 m². Thus, Q = 0.0314 × 2 = 0.0628 m³/s.
Description: Discharge Q = A × v. Area A = πr² = π(0.1)² = 0.0314 m². Thus, Q = 0.0314 × 2 = 0.0628 m³/s.
9. Which statement is correct about laminar flow?
Answer: c) It is characterized by smooth, parallel layers
Description: Laminar flow occurs at low Reynolds numbers (Re < 2000 for pipes), where fluid moves in smooth, parallel layers with minimal mixing, unlike turbulent flow.
Description: Laminar flow occurs at low Reynolds numbers (Re < 2000 for pipes), where fluid moves in smooth, parallel layers with minimal mixing, unlike turbulent flow.
10. The buoyant force on an object immersed in a fluid is equal to:
Answer: b) The weight of the fluid displaced
Description: Archimedes’ principle states that the buoyant force equals the weight of the fluid displaced by the object, given by F_b = ρ_f × V × g.
Description: Archimedes’ principle states that the buoyant force equals the weight of the fluid displaced by the object, given by F_b = ρ_f × V × g.
11. A centrifugal pump delivers water at 0.1 m³/s against a head of 20 m. If the efficiency is 80%, what is the power required (ρ = 1000 kg/m³, g = 9.81 m/s²)?
Answer: b) 3.06 kW
Description: Hydraulic power P_h = ρgQH = 1000 × 9.81 × 0.1 × 20 = 19620 W. Actual power P = P_h/η = 19620/0.8 = 24525 W = 3.06 kW.
Description: Hydraulic power P_h = ρgQH = 1000 × 9.81 × 0.1 × 20 = 19620 W. Actual power P = P_h/η = 19620/0.8 = 24525 W = 3.06 kW.
12. Which of the following is NOT a type of hydraulic turbine?
Answer: d) Venturi
Description: Pelton, Francis, and Kaplan are types of hydraulic turbines used for power generation. Venturi refers to a device for measuring flow rate, not a turbine.
Description: Pelton, Francis, and Kaplan are types of hydraulic turbines used for power generation. Venturi refers to a device for measuring flow rate, not a turbine.
13. The specific speed of a turbine is defined as:
Answer: a) Speed at which the turbine delivers unit power under unit head
Description: Specific speed N_s = N√P/H^(5/4), where N is speed, P is power, and H is head. It characterizes turbine type based on performance under standardized conditions.
Description: Specific speed N_s = N√P/H^(5/4), where N is speed, P is power, and H is head. It characterizes turbine type based on performance under standardized conditions.
14. A rectangular channel has a width of 2 m and depth of 1 m. If the velocity is 1.5 m/s, calculate the discharge.
Answer: a) 3 m³/s
Description: Discharge Q = A × v. Area A = width × depth = 2 × 1 = 2 m². Thus, Q = 2 × 1.5 = 3 m³/s.
Description: Discharge Q = A × v. Area A = width × depth = 2 × 1 = 2 m². Thus, Q = 2 × 1.5 = 3 m³/s.
15. Cavitation in hydraulic machines occurs due to:
Answer: b) Low pressure
Description: Cavitation occurs when the local pressure drops below the vapor pressure, causing vapor bubbles to form and collapse, potentially damaging machine components.
Description: Cavitation occurs when the local pressure drops below the vapor pressure, causing vapor bubbles to form and collapse, potentially damaging machine components.
16. Which of the following statements about turbulent flow is true?
Answer: b) It is characterized by random particle motion
Description: Turbulent flow (Re > 4000 for pipes) involves chaotic, random motion of fluid particles, leading to mixing, unlike laminar flow’s orderly motion.
Description: Turbulent flow (Re > 4000 for pipes) involves chaotic, random motion of fluid particles, leading to mixing, unlike laminar flow’s orderly motion.
17. The Euler’s equation of motion is derived from:
Answer: b) Conservation of momentum
Description: Euler’s equation relates pressure, velocity, and density along a streamline, derived from Newton’s second law (momentum conservation) for inviscid flow.
Description: Euler’s equation relates pressure, velocity, and density along a streamline, derived from Newton’s second law (momentum conservation) for inviscid flow.
18. A Pelton wheel operates under a head of 100 m and delivers 500 kW. If the efficiency is 85%, what is the discharge (ρ = 1000 kg/m³, g = 9.81 m/s²)?
Answer: a) 0.06 m³/s
Description: Power P = η × ρgQH. Given P = 500000 W, η = 0.85, ρ = 1000 kg/m³, g = 9.81 m/s², H = 100 m, solve for Q: 500000 = 0.85 × 1000 × 9.81 × Q × 100. Thus, Q = 500000/(0.85 × 981000) ≈ 0.06 m³/s.
Description: Power P = η × ρgQH. Given P = 500000 W, η = 0.85, ρ = 1000 kg/m³, g = 9.81 m/s², H = 100 m, solve for Q: 500000 = 0.85 × 1000 × 9.81 × Q × 100. Thus, Q = 500000/(0.85 × 981000) ≈ 0.06 m³/s.
19. The term ‘hydraulic jump’ refers to:
Answer: b) A sudden increase in fluid depth
Description: A hydraulic jump occurs in open channel flow when supercritical flow (high velocity, low depth) transitions to subcritical flow (low velocity, high depth), causing a sudden depth increase.
Description: A hydraulic jump occurs in open channel flow when supercritical flow (high velocity, low depth) transitions to subcritical flow (low velocity, high depth), causing a sudden depth increase.
20. Which of the following is a positive displacement pump?
Answer: b) Reciprocating pump
Description: Positive displacement pumps deliver a fixed volume per cycle, e.g., reciprocating pumps. Centrifugal, axial flow, and propeller pumps are dynamic pumps.
Description: Positive displacement pumps deliver a fixed volume per cycle, e.g., reciprocating pumps. Centrifugal, axial flow, and propeller pumps are dynamic pumps.
21. The pressure head in a fluid flow is given by:
Answer: a) P/ρg
Description: Pressure head represents the height of a fluid column that a given pressure can support, given by P/ρg, where P is pressure, ρ is density, and g is gravitational acceleration.
Description: Pressure head represents the height of a fluid column that a given pressure can support, given by P/ρg, where P is pressure, ρ is density, and g is gravitational acceleration.
22. A pipe carries water at 0.05 m³/s. If the diameter is 0.1 m, what is the average velocity?
Answer: a) 6.37 m/s
Description: Velocity v = Q/A. Area A = πr² = π(0.05)² = 0.00785 m². Thus, v = 0.05/0.00785 ≈ 6.37 m/s.
Description: Velocity v = Q/A. Area A = πr² = π(0.05)² = 0.00785 m². Thus, v = 0.05/0.00785 ≈ 6.37 m/s.
23. Which of the following is true for an ideal fluid?
Answer: b) It is incompressible and inviscid
Description: An ideal fluid is a theoretical fluid with zero viscosity (inviscid) and constant density (incompressible), simplifying flow analysis.
Description: An ideal fluid is a theoretical fluid with zero viscosity (inviscid) and constant density (incompressible), simplifying flow analysis.
24. The Darcy-Weisbach equation is used to calculate:
Answer: b) Head loss due to friction
Description: The Darcy-Weisbach equation, h_f = f(L/D)(v²/2g), calculates head loss due to friction in pipes, where f is the friction factor, L is length, D is diameter, and v is velocity.
Description: The Darcy-Weisbach equation, h_f = f(L/D)(v²/2g), calculates head loss due to friction in pipes, where f is the friction factor, L is length, D is diameter, and v is velocity.
25. A Kaplan turbine is suitable for:
Answer: b) Low head, high discharge
Description: Kaplan turbines are axial-flow turbines designed for low head (e.g., 10–50 m) and high discharge, commonly used in large river hydropower plants.
Description: Kaplan turbines are axial-flow turbines designed for low head (e.g., 10–50 m) and high discharge, commonly used in large river hydropower plants.
26. The velocity head in a fluid flow is given by:
Answer: a) v²/2g
Description: Velocity head represents the kinetic energy per unit weight of a fluid, given by v²/2g, where v is velocity and g is gravitational acceleration.
Description: Velocity head represents the kinetic energy per unit weight of a fluid, given by v²/2g, where v is velocity and g is gravitational acceleration.
27. A venturimeter is used to measure:
Answer: b) Discharge
Description: A venturimeter measures the flow rate (discharge) in a pipe by applying Bernoulli’s equation and the continuity equation to the pressure difference across a constricted section.
Description: A venturimeter measures the flow rate (discharge) in a pipe by applying Bernoulli’s equation and the continuity equation to the pressure difference across a constricted section.
28. A body floats in water with 40% of its volume submerged. What is the specific gravity of the body?
Answer: a) 0.4
Description: For a floating body, the fraction submerged equals the specific gravity (SG) of the body relative to water. If 40% is submerged, SG = 0.4.
Description: For a floating body, the fraction submerged equals the specific gravity (SG) of the body relative to water. If 40% is submerged, SG = 0.4.
29. Which of the following is true about a reciprocating pump?
Answer: b) It is suitable for high heads
Description: Reciprocating pumps are positive displacement pumps suitable for high heads and low discharge. Discharge may vary, and they have moving parts (piston/cylinder).
Description: Reciprocating pumps are positive displacement pumps suitable for high heads and low discharge. Discharge may vary, and they have moving parts (piston/cylinder).
30. The Manning’s formula is used in:
Answer: b) Open channel flow
Description: Manning’s formula, v = (1/n)R^(2/3)S^(1/2), calculates velocity in open channel flow, where n is roughness coefficient, R is hydraulic radius, and S is slope.
Description: Manning’s formula, v = (1/n)R^(2/3)S^(1/2), calculates velocity in open channel flow, where n is roughness coefficient, R is hydraulic radius, and S is slope.
31. A fluid flows through a pipe of diameter 0.15 m at a velocity of 3 m/s. What is the Reynolds number (μ = 0.001 N·s/m², ρ = 1000 kg/m³)?
Answer: b) 45000
Description: Reynolds number Re = ρvD/μ. Substituting ρ = 1000 kg/m³, v = 3 m/s, D = 0.15 m, μ = 0.001 N·s/m², Re = (1000 × 3 × 0.15)/0.001 = 45000.
Description: Reynolds number Re = ρvD/μ. Substituting ρ = 1000 kg/m³, v = 3 m/s, D = 0.15 m, μ = 0.001 N·s/m², Re = (1000 × 3 × 0.15)/0.001 = 45000.
32. The term ‘stagnation pressure’ refers to:
Answer: a) Pressure at zero velocity
Description: Stagnation pressure is the total pressure at a point where the fluid velocity is zero, combining static pressure and dynamic pressure (ρv²/2).
Description: Stagnation pressure is the total pressure at a point where the fluid velocity is zero, combining static pressure and dynamic pressure (ρv²/2).
33. Which of the following is a similarity parameter in model testing?
Answer: a) Froude number
Description: Froude number (Fr = v/√(gL)) is a dimensionless similarity parameter used in model testing to ensure dynamic similarity, especially for free surface flows.
Description: Froude number (Fr = v/√(gL)) is a dimensionless similarity parameter used in model testing to ensure dynamic similarity, especially for free surface flows.
34. A hydraulic ram is a device used to:
Answer: b) Pump water using water hammer
Description: A hydraulic ram uses the water hammer effect to pump a portion of water to a higher elevation without external power, leveraging kinetic energy.
Description: A hydraulic ram uses the water hammer effect to pump a portion of water to a higher elevation without external power, leveraging kinetic energy.
35. The Chezy’s formula is used to calculate:
Answer: b) Velocity in open channels
Description: Chezy’s formula, v = C√(R·S), calculates velocity in open channel flow, where C is Chezy’s constant, R is hydraulic radius, and S is slope.
Description: Chezy’s formula, v = C√(R·S), calculates velocity in open channel flow, where C is Chezy’s constant, R is hydraulic radius, and S is slope.
36. A pipe has a head loss of 5 m over a length of 100 m. If the discharge is 0.02 m³/s, what is the diameter (f = 0.02, g = 9.81 m/s²)?
Answer: b) 0.15 m
Description: Using Darcy-Weisbach, h_f = f(L/D)(v²/2g). Velocity v = Q/A = Q/(πD²/4). Substituting h_f = 5 m, L = 100 m, f = 0.02, Q = 0.02 m³/s, solve for D: 5 = 0.02 × (100/D) × [(0.02/(πD²/4))²/(2 × 9.81)]. Trial yields D ≈ 0.15 m.
Description: Using Darcy-Weisbach, h_f = f(L/D)(v²/2g). Velocity v = Q/A = Q/(πD²/4). Substituting h_f = 5 m, L = 100 m, f = 0.02, Q = 0.02 m³/s, solve for D: 5 = 0.02 × (100/D) × [(0.02/(πD²/4))²/(2 × 9.81)]. Trial yields D ≈ 0.15 m.
37. Which of the following is true about a Francis turbine?
Answer: b) It is suitable for medium head
Description: Francis turbines are reaction turbines suitable for medium head (50–250 m) and medium discharge. They have radial or mixed flow, unlike axial Kaplan turbines.
Description: Francis turbines are reaction turbines suitable for medium head (50–250 m) and medium discharge. They have radial or mixed flow, unlike axial Kaplan turbines.
38. The hydraulic gradient line represents:
Answer: b) Pressure head plus elevation head
Description: The hydraulic gradient line (HGL) shows the sum of pressure head (P/ρg) and elevation head (z), excluding velocity head, unlike the total energy line.
Description: The hydraulic gradient line (HGL) shows the sum of pressure head (P/ρg) and elevation head (z), excluding velocity head, unlike the total energy line.
39. A jet of water strikes a flat plate with a velocity of 10 m/s and a discharge of 0.01 m³/s. What is the force on the plate if it is stationary?
Answer: a) 100 N
Description: Force F = ρQv, where ρ = 1000 kg/m³, Q = 0.01 m³/s, v = 10 m/s. Thus, F = 1000 × 0.01 × 10 = 100 N.
Description: Force F = ρQv, where ρ = 1000 kg/m³, Q = 0.01 m³/s, v = 10 m/s. Thus, F = 1000 × 0.01 × 10 = 100 N.
40. The term ‘draft tube’ is associated with:
Answer: b) Reaction turbines
Description: A draft tube is used in reaction turbines (e.g., Francis, Kaplan) to recover kinetic energy at the turbine exit and increase efficiency by reducing exit velocity.
Description: A draft tube is used in reaction turbines (e.g., Francis, Kaplan) to recover kinetic energy at the turbine exit and increase efficiency by reducing exit velocity.
41. Which of the following is a unit of specific weight?
Answer: a) N/m³
Description: Specific weight (γ = ρg) is the weight per unit volume, with units N/m³. Density uses kg/m³, and pressure uses N/m².
Description: Specific weight (γ = ρg) is the weight per unit volume, with units N/m³. Density uses kg/m³, and pressure uses N/m².
42. A fluid has a specific gravity of 0.8. What is its density?
Answer: a) 800 kg/m³
Description: Specific gravity is the ratio of a fluid’s density to water’s density (1000 kg/m³). Thus, density = SG × 1000 = 0.8 × 1000 = 800 kg/m³.
Description: Specific gravity is the ratio of a fluid’s density to water’s density (1000 kg/m³). Thus, density = SG × 1000 = 0.8 × 1000 = 800 kg/m³.
43. Which of the following is true about an impulse turbine?
Answer: b) It uses the kinetic energy of a jet
Description: Impulse turbines (e.g., Pelton) convert the kinetic energy of a high-velocity jet into mechanical work, typically under high head, and are not submerged.
Description: Impulse turbines (e.g., Pelton) convert the kinetic energy of a high-velocity jet into mechanical work, typically under high head, and are not submerged.
44. The hydraulic efficiency of a turbine is defined as:
Answer: c) Ratio of runner power to water power
Description: Hydraulic efficiency η_h = (power delivered to runner)/(water power) = P_r/(ρgQH), measuring how effectively the turbine converts water energy to mechanical energy.
Description: Hydraulic efficiency η_h = (power delivered to runner)/(water power) = P_r/(ρgQH), measuring how effectively the turbine converts water energy to mechanical energy.
45. A pipe network follows which of the following principles?
Answer: b) Conservation of mass and energy
Description: Pipe networks obey conservation of mass (continuity) at junctions and conservation of energy (Bernoulli’s equation, adjusted for losses) across the system.
Description: Pipe networks obey conservation of mass (continuity) at junctions and conservation of energy (Bernoulli’s equation, adjusted for losses) across the system.
46. A centrifugal pump has a specific speed of 50. It is best suited for:
Answer: a) High head, low discharge
Description: Low specific speed (e.g., 50) centrifugal pumps are radial flow pumps suited for high head and low discharge, unlike high specific speed pumps for low head, high discharge.
Description: Low specific speed (e.g., 50) centrifugal pumps are radial flow pumps suited for high head and low discharge, unlike high specific speed pumps for low head, high discharge.
47. The term ‘boundary layer’ refers to:
Answer: b) The region near a surface where viscosity effects are significant
Description: The boundary layer is the thin region near a solid surface where the fluid velocity transitions from zero (at the surface) to the free stream value, dominated by viscous effects.
Description: The boundary layer is the thin region near a solid surface where the fluid velocity transitions from zero (at the surface) to the free stream value, dominated by viscous effects.
48. A turbine has a power output of 1000 kW under a head of 50 m. If the discharge is 2 m³/s, what is the overall efficiency (ρ = 1000 kg/m³, g = 9.81 m/s²)?
Answer: a) 81.5%
Description: Overall efficiency η = P/(ρgQH). Given P = 1000000 W, ρ = 1000 kg/m³, g = 9.81 m/s², Q = 2 m³/s, H = 50 m, η = 1000000/(1000 × 9.81 × 2 × 50) ≈ 0.815 or 81.5%.
Description: Overall efficiency η = P/(ρgQH). Given P = 1000000 W, ρ = 1000 kg/m³, g = 9.81 m/s², Q = 2 m³/s, H = 50 m, η = 1000000/(1000 × 9.81 × 2 × 50) ≈ 0.815 or 81.5%.
49. Which of the following devices is used to measure pressure difference?
Answer: b) Manometer
Description: A manometer directly measures pressure difference between two points in a fluid. Orifice meters and venturimeters measure flow rate, pitot tubes measure velocity, and rotameters measure flow rate visually.
Description: A manometer directly measures pressure difference between two points in a fluid. Orifice meters and venturimeters measure flow rate, pitot tubes measure velocity, and rotameters measure flow rate visually.
50. The specific energy in an open channel flow is minimum at:
Answer: c) Critical flow
Description: Specific energy (E = y + v²/2g) is minimum at critical flow, where the Froude number is 1, and the flow depth is critical, balancing kinetic and potential energy.
Description: Specific energy (E = y + v²/2g) is minimum at critical flow, where the Froude number is 1, and the flow depth is critical, balancing kinetic and potential energy.