Fluid Mechanics MCQ Practice Set — 50 Questions with Answers
50 exam-oriented Fluid Mechanics multiple-choice questions with the correct answer and a clear explanation for each. Frequently asked in AE Level Civil Engineering, JE Level Civil Engineering. Solve the full set below for free — no login required.
- 1Fluid MechanicsHARD
The 'draft tube' in a reaction turbine (Francis/Kaplan) serves to:
ASupply water to the turbine from the reservoirBRecover kinetic energy at runner exit AND allow turbine above tailwater level — maintains full net head utilisationCRegulate turbine speedDFilter debris from waterAnswer: B. Recover kinetic energy at runner exit AND allow turbine above tailwater level — maintains full net head utilisation
Explanation: Draft tube: diverging passage connecting runner exit to tailrace. Functions: (1) Converts kinetic energy at runner exit to pressure (reduces exit velocity loss); (2) Allows turbine to be set ABOVE tailwater level without losing net head (creates suction at runner by extending head through draft tube). Recovery: velocity head at runner exit (V²/2g) recovered. Without draft tube: runner exit velocity wasted.
- 2Fluid MechanicsMEDIUM
The 'specific energy' in open channel flow is:
ATotal energy above datum E = p/γ + V²/2g + zBE = y + V²/2g — depth plus velocity head measured from channel invert; minimum at critical depthCE = V²/2g only (no depth term)DE = y (depth only at zero velocity)Answer: B. E = y + V²/2g — depth plus velocity head measured from channel invert; minimum at critical depth
Explanation: Specific energy E = y + V²/(2g) = y + Q²/(2gA²). At critical depth y_c: E is minimum for given Q. For rectangular channel: y_c = (q²/g)^(1/3), E_min = 3y_c/2. E-y curve: two limbs (subcritical upper, supercritical lower). At given E (> E_min): two possible depths (subcritical and supercritical) — conjugate depths. Critical flow: Fr=1. Used for: sluice gate analysis, drop structure, channel transitions.
- 3Fluid MechanicsMEDIUM
The 'tsunami' is distinguished from wind waves by:
ATsunami is caused by wind like ordinary wavesBSeismically generated; very long wavelength (shallow water wave); travels at √(gd) ≈ 700 km/h; arrives as series of wavesCTsunami is only tidal in originDNo difference from storm waves in deep waterAnswer: B. Seismically generated; very long wavelength (shallow water wave); travels at √(gd) ≈ 700 km/h; arrives as series of waves
Explanation: Tsunami: seismically generated ocean wave (earthquake, submarine landslide, volcanic). Very long wavelength (100–600 km → shallow water wave everywhere L >> 10d); very long period (10 min to 2 hours); speed C = √(gd) — 700 km/h in deep ocean. In open ocean: amplitude 0.3–1 m (undetectable). Near shore: shoaling amplifies height to 10–30 m. Run-up: penetrates inland. Warning: DART buoy + seismic monitoring.
- 4Fluid MechanicsMEDIUM
Two identical pumps in 'series' vs. 'parallel' connection:
ASeries gives double flow; parallel gives double headBSeries: heads add (2H); parallel: flows add (2Q) — choice depends on high-head vs. high-flow requirementCBoth series and parallel give same resultDSeries reduces head and increases flowAnswer: B. Series: heads add (2H); parallel: flows add (2Q) — choice depends on high-head vs. high-flow requirement
Explanation: Two identical pumps: (1) Series: heads ADD, flow same → total H = 2H_single at same Q; used for high head, moderate flow (borewell multistage pumps). (2) Parallel: flows ADD, head same → total Q = 2Q_single at same H; used for high flow, moderate head (water supply distribution). System operating point: intersection of combined pump curve with system H-Q curve. Parallel effective only if system curve is flat.
- 5Fluid MechanicsMEDIUM
The 'cavitation' damage to hydraulic turbines and pump impellers appears as:
AUniform smooth wear over entire bladeBPitting (small craters) from implosion shockwaves on blade surfaces — progressive material loss changes blade profileCCorrosion from dissolved saltsDThermal expansion cracksAnswer: B. Pitting (small craters) from implosion shockwaves on blade surfaces — progressive material loss changes blade profile
Explanation: Cavitation damage: implosion of vapour bubbles on solid surface releases high-pressure shockwaves + micro-jets → pitting (small craters) on metal surface. Progressive pitting → loss of material → change in blade profile → reduced efficiency → vibration. Cavitation index σ = (Hatm − Hvapour − Hs)/H used to assess risk. Prevented by: limit suction head, stainless steel or cavitation-resistant material, coatings.
- 6Fluid MechanicsMEDIUM
The 'flow net' for seepage analysis consists of:
AOnly equipotential linesBFlow lines + equipotential lines forming curvilinear squares (90° intersections) — q = kH×Nf/Nd per unit widthCOnly velocity vectorsDPressure distribution diagram aloneAnswer: B. Flow lines + equipotential lines forming curvilinear squares (90° intersections) — q = kH×Nf/Nd per unit width
Explanation: Flow net: graphical solution to Laplace equation (∇²h = 0) for potential flow. Consists of: (1) Flow lines (stream lines — paths of water particle); (2) Equipotential lines (lines of equal head). Properties: flow lines and equipotential lines intersect at RIGHT ANGLES (conformal mapping). Curvilinear squares (a = b) for uniform q. q = kH × Nf/Nd per unit width where Nf = flow channels, Nd = equipotential drops.
- 7Fluid MechanicsHARD
The 'littoral drift' along a coastline is the movement of sediment caused by:
AOnly rainfall runoff carrying sand to seaBOblique wave breaking and swash/backwash asymmetry — waves at angle to shore drive longshore transport of sedimentCOnly tidal currents perpendicular to shoreDWind blowing onshore at any angleAnswer: B. Oblique wave breaking and swash/backwash asymmetry — waves at angle to shore drive longshore transport of sediment
Explanation: Littoral drift (longshore sediment transport): sediment carried along coast by oblique wave approach. When waves approach at angle to shore → oblique swash carries sediment up-beach at angle → backwash returns perpendicular → net transport along coast. Rates: 100,000–2,000,000 m³/year on sandy coasts. Interrupted by: jetties, groins, ports → downdrift erosion. CERC formula for longshore sediment transport rate.
- 8Fluid MechanicsMEDIUM
The 'Darcy-Weisbach' equation for head loss hf in a pipe is:
Ahf = V²/2g only (velocity head)Bhf = f×(L/D)×V²/(2g) — Darcy-Weisbach with Moody chart friction factor f; fundamental for all pipe flowChf = 10.67×L×Q^1.85/(C^1.85×D^4.87) (Hazen-Williams, not Darcy-Weisbach)Dhf = f×L (no velocity or diameter term)Answer: B. hf = f×(L/D)×V²/(2g) — Darcy-Weisbach with Moody chart friction factor f; fundamental for all pipe flow
Explanation: Darcy-Weisbach: hf = f×(L/D)×V²/(2g) = f×L×Q²/(12.1×D⁵) (practical form). Friction factor f: Moody chart — laminar: f = 64/Re; turbulent smooth: Blasius f = 0.316/Re^0.25; turbulent rough: Colebrook-White (implicit) or Swamee-Jain (explicit). L = pipe length (m), D = diameter (m). Fundamental equation, unlike Hazen-Williams which is empirical. HW: V = 0.849×C×R^0.63×S^0.54 (C = HW coefficient, empirical for water).
- 9Fluid MechanicsMEDIUM
The 'specific speed' Ns of a turbine is used to classify the type:
ASpecific speed only determines blade materialBClassifies turbine type: Pelton (low Ns, high head), Francis (medium), Kaplan (high Ns, low head)CSpecific speed is only for pumps, not turbinesDHigher Ns always means higher efficiencyAnswer: B. Classifies turbine type: Pelton (low Ns, high head), Francis (medium), Kaplan (high Ns, low head)
Explanation: Turbine specific speed Ns = N√P / H^(5/4) (with consistent units). OR Nq = N√Q / H^(3/4) (flow-based). Classification: (1) Pelton (impulse): Ns = 10–35 (high head 200–2000 m); (2) Francis (reaction, mixed flow): Ns = 50–300 (medium head 50–600 m); (3) Kaplan (axial flow): Ns = 300–900 (low head 5–70 m). High Ns → low head, high flow; Low Ns → high head, low flow. Specific speed: dimensionless parameter selecting turbine type.
- 10Fluid MechanicsMEDIUM
A 'rubble mound breakwater' resists wave attack primarily by:
AReflection (acts like a vertical wall)BWave energy absorption through permeability, armour interlocking, and rough slope dissipation — not reflectionCSuction removing wave energyDSteel sheet piling resisting impactAnswer: B. Wave energy absorption through permeability, armour interlocking, and rough slope dissipation — not reflection
Explanation: Rubble mound breakwater: core of quarry run stone + armour layer of large rock or concrete units (Tetrapods, Accropode, Core-Loc). Wave energy dissipated by: (1) Permeability (water infiltrates through voids, energy absorbed); (2) Armour unit interlocking (individual units don''t slide due to friction and form); (3) Wave run-up on rough, permeable slope. Hudson formula: W50 = γr×H³/(KD×(γr/γw-1)³×cotα) for armour weight.
- 11Fluid MechanicsMEDIUM
The 'scour' at a bridge pier is caused by:
AOnly during low-flow conditionsBHorseshoe vortex at pier base + increased velocities in contracted waterway erode river bed materialCOnly from earthquake ground motionDScour is beneficial for bridge safetyAnswer: B. Horseshoe vortex at pier base + increased velocities in contracted waterway erode river bed material
Explanation: Bridge pier scour: local erosion of river bed around pier due to increased flow velocities and horseshoe vortex formation at pier base. Types: (1) General scour (bed lowering from floods); (2) Contraction scour (narrowing of waterway between piers accelerates flow); (3) Local scour (horseshoe vortex at pier nose). Design: total scour = general + contraction + local. HEC-18 (US) / IS 3955 covers scour depth estimation.
- 12Fluid MechanicsMEDIUM
The 'storm surge' phenomenon along coasts is caused by:
ARegular tidal oscillation onlyBCyclonic wind setup + low pressure (inverse barometer) + wave setup raising sea level above predicted tideCSubmarine earthquake (tsunami — different phenomenon)DRiver floods flowing into the seaAnswer: B. Cyclonic wind setup + low pressure (inverse barometer) + wave setup raising sea level above predicted tide
Explanation: Storm surge: rise in sea level above predicted tide during tropical cyclone/storm. Caused by: (1) Wind setup (onshore wind pushes water toward coast); (2) Low atmospheric pressure (inverse barometer: 1 hPa drop ≈ 1 cm sea rise); (3) Wave setup (wave momentum transferred to increase mean water level). Surge height: 1–7 m for major cyclones. Andhra/Odisha coast historically vulnerable (shallow bathymetry amplifies surge).
- 13Fluid MechanicsHARD
The 'Joukowski' pressure rise due to water hammer when a valve closes instantaneously is:
AΔP = ρ × V² / 2 (dynamic pressure only)BΔP = ρ × c × ΔV — wave speed c (~1000 m/s for steel pipe) × density × velocity change; very large for fast closureCΔP = c × V only (no density term)DΔP is always less than 0.1 barAnswer: B. ΔP = ρ × c × ΔV — wave speed c (~1000 m/s for steel pipe) × density × velocity change; very large for fast closure
Explanation: Joukowski (1898): ΔP = ρ × c × ΔV where ρ = water density, c = wave speed = √(K/ρ) modified for pipe elasticity (typically c = 800–1200 m/s for steel pipes), ΔV = change in velocity at valve. For instantaneous closure from V to 0: ΔP = ρcV. Example: ρ=1000, c=1000 m/s, V=2 m/s → ΔP = 2×10⁶ Pa = 2 MPa. Wave travels upstream at speed c. Protection: slow valve closure (T > 2L/c — critical time), surge tanks, pressure relief valves.
- 14Fluid MechanicsHARD
The 'Stokes'' wave' theory (finite amplitude) differs from Airy theory in that Stokes'' theory accounts for:
AOnly tidal effects at long periodsBNon-linear effects: asymmetric wave profile (sharp crest, flat trough) and net Stokes drift in wave directionCLinear relationships between all wave parametersDStokes removes Airy''s assumptions about pressureAnswer: B. Non-linear effects: asymmetric wave profile (sharp crest, flat trough) and net Stokes drift in wave direction
Explanation: Stokes higher-order wave theory: includes non-linear effects. Differences from Airy (1st order): (1) Wave crest sharper, trough flatter (non-sinusoidal profile); (2) Net drift of water particles in wave direction (Stokes drift); (3) Wave speed depends on amplitude (slightly faster for higher waves); (4) Set-up and set-down effects. 2nd order Stokes: accurate for intermediate waves. Breaking criterion: H/L > 0.142 or H/d > 0.78.
- 15Fluid MechanicsMEDIUM
The 'Tainter gate' (radial gate) on a dam spillway has the advantage that:
ATainter gate has larger gate area than vertical gateBWater pressure resultant passes through trunnion pivot → zero net moment → small hoist force needed (very efficient for large heads)CIt does not require any maintenanceDOnly works in closed position, cannot be opened partiallyAnswer: B. Water pressure resultant passes through trunnion pivot → zero net moment → small hoist force needed (very efficient for large heads)
Explanation: Tainter gate: curved skin plate on radial arm pivoted at trunnion (fixed point on pier). Advantage: hydraulic reaction from water pressure passes through trunnion → no net moment → very small hoisting force needed. Contrast: vertical lift gate must lift against full water pressure. Large sizes: 20×15 m common. Used on: spillway crests, navigation locks, canal head regulators. Seal: rubber seals at sides and sill. Self-regulating variant: Fuseplug.
- 16Fluid MechanicsMEDIUM
The 'hydraulic grade line' (HGL) in a pressurised pipe:
ATotal energy line including velocity headBPiezometric head (p/γ + z) at each point — represents pressure head only; below pipe = negative pressure/cavitationCVelocity profile at each sectionDPipe centreline elevation profileAnswer: B. Piezometric head (p/γ + z) at each point — represents pressure head only; below pipe = negative pressure/cavitation
Explanation: HGL: locus of points to which water would rise in piezometric tubes — represents p/γ + z at each section. Plotted above pipe: pressure positive (normal). Falls below pipe: negative pressure (vacuum → cavitation risk). HGL slope = −hf/L = hydraulic gradient. EGL (energy grade line) = HGL + V²/2g — always above HGL (kinetic head). HGL falls: friction losses, flow acceleration. HGL rises: pump adds energy; pressure recovery in decelerating flow.
- 17Fluid MechanicsMEDIUM
'Flow measurement' by an electromagnetic (EM) flowmeter relies on:
APressure difference across an orificeBFaraday''s law: conductive fluid in magnetic field generates EMF ∝ velocity — no pressure drop, works with slurriesCCounting bubbles in flowDSonic pulses reflected by particlesAnswer: B. Faraday''s law: conductive fluid in magnetic field generates EMF ∝ velocity — no pressure drop, works with slurries
Explanation: EM flowmeter: Faraday''s law of induction — electrically conducting liquid flowing through magnetic field generates EMF proportional to velocity. E = B×D×V (E = EMF, B = magnetic flux, D = pipe diameter). Requires: electrically conductive fluid (water, sewage, slurry — minimum σ ~ 5 μS/cm). Not for: petroleum (non-conducting) — use Coriolis. Advantages: no moving parts, zero pressure drop, measures any direction, works with solids-laden flow.
- 18Fluid MechanicsMEDIUM
The 'Moody diagram' relates the friction factor f to:
AOnly pipe material and pressureBReynolds number Re and relative roughness ks/D — determines Darcy friction factor for all pipe flow regimesCOnly flow velocity and pipe diameter aloneDPipe age and corrosion categoryAnswer: B. Reynolds number Re and relative roughness ks/D — determines Darcy friction factor for all pipe flow regimes
Explanation: Moody diagram: plot of Darcy-Weisbach friction factor f vs. Reynolds number Re for different relative roughness (ks/D) values. Regions: (1) Laminar (Re < 2000): f = 64/Re (straight line, independent of roughness); (2) Transition (2000–4000): unstable; (3) Turbulent smooth (Blasius); (4) Fully rough turbulent: f depends only on ks/D (independent of Re); (5) Transition turbulent: Colebrook-White equation covers this. Essential tool for pipe hydraulics.
- 19Fluid MechanicsHARD
The 'Mach number' becomes important in fluid mechanics when:
AIn all flow of water regardless of velocityBWhen V approaches speed of sound (Ma > 0.3) — density changes significant; not usually relevant in water flow or low-speed airCOnly for laminar flowDWhen Reynolds number exceeds 10⁶Answer: B. When V approaches speed of sound (Ma > 0.3) — density changes significant; not usually relevant in water flow or low-speed air
Explanation: Mach number Ma = V/c where c = speed of sound = √(γRT) for ideal gas. Ma < 0.3: incompressible flow (density changes < 5%, can ignore). Ma 0.3–0.8: subsonic compressible. Ma ~ 1.0: transonic. Ma > 1.0: supersonic (shock waves). Ma > 5: hypersonic. Civil engineering: almost all applications use water or slow air → Ma << 0.3 → incompressible → Mach number irrelevant. Relevant in: pneumatic conveying, gas pipelines at high velocity, aerodynamic forces on tall buildings in special cases.
- 20Original practiceMEDIUM
The gauge pressure at a depth of 2 m below free surface of water is approximately
A9.81 kPaB39.24 kPaC29.43 kPaD19.62 kPaAnswer: D. 19.62 kPa
Explanation: Gauge pressure at depth h below a free water surface: p = γ × h = ρ × g × h. For water, unit weight γ = 9.81 kN/m³. At h = 2 m: p = 9.81 × 2 = 19.62 kPa kPa. Gauge pressure is measured relative to atmospheric pressure and increases linearly with depth.
- 21GeneralMEDIUM
The hydraulic gradient line in pipe flow represents
Apiezometric head lineBwater surface of reservoir onlyCpipe invert lineDtotal energy line including velocity headAnswer: A. piezometric head line
Explanation: Hydraulic Grade Line (HGL) = piezometric head = pressure head (p/gamma_w) + datum head (z). Total Energy Line (TEL/EGL) = piezometric head + velocity head (V^2/2g). TEL lies above HGL by the velocity head at every section. HGL can fall below the pipe invert if pressure becomes sub-atmospheric (risk of cavitation or pipe collapse). HGL is pressure head plus datum head.
- 22Darcy WeisbachMEDIUM
For fully turbulent flow in a rough pipe, the Darcy friction factor f is determined by the:
AReynolds number onlyBRelative roughness e/D onlyCBoth Re and e/D (Moody chart)DPipe material densityAnswer: B. Relative roughness e/D only
Explanation: In the fully rough turbulent flow regime (high Reynolds number), the friction factor becomes independent of the Reynolds number and depends only on the relative roughness (e/D) as described by the Nikuradse or Colebrook-White equations.
- 23Fluid MechanicsMEDIUM
The size of a centrifugal water pump is typically designated by:
AHorsepowerBImpeller diameterCDischargeDSuction and delivery pipe diameterAnswer: D. Suction and delivery pipe diameter
Explanation: In engineering practice, the nominal size of a centrifugal pump is designated by the diameter of its suction and delivery nozzles (pipe connections).
- 24Pipe FlowHARD
Water hammer pressure rise when valve closes rapidly: ΔP = ρ×a×ΔV, where a = wave speed. For ρ=1000 kg/m³, a=1200 m/s, ΔV=2 m/s:
A2.4 MPaB24 MPaC0.24 MPaD120 kPaAnswer: A. 2.4 MPa
Explanation: ΔP = ρ×a×ΔV = 1000×1200×2 = 2,400,000 Pa = 2.4 MPa. This is the Joukowsky (Zhukovsky) equation for instantaneous valve closure.
- 25Fluid MechanicsEASY
The 'piezometric surface' of a confined aquifer is the imaginary surface to which water rises in:
AAll open channels at the surfaceBPiezometers (tightly cased observation wells) penetrating the confined aquifer — water level indicates pressure headCOnly streams and riversDWater table in adjacent unconfined aquiferAnswer: B. Piezometers (tightly cased observation wells) penetrating the confined aquifer — water level indicates pressure head
Explanation: Piezometric surface (potentiometric surface): imaginary surface joining the water levels in tightly cased wells (piezometers) penetrating a confined aquifer. If piezometric surface is above ground level: artesian well (water flows without pumping). If below ground: sub-artesian (must pump but requires less lift than water table well of same depth). Confined aquifer is always saturated.
- 26Fluid MechanicsMEDIUM
The 'coefficient of transmissivity' T of an aquifer is defined as:
APermeability k aloneBT = k × b — hydraulic conductivity × saturated thickness; governs well yield and aquifer drawdownCOnly the aquifer thickness bDPorosity × thicknessAnswer: B. T = k × b — hydraulic conductivity × saturated thickness; governs well yield and aquifer drawdown
Explanation: Transmissivity T = k × b (m²/day or m²/s) where k = hydraulic conductivity, b = saturated thickness of aquifer. T represents the rate of groundwater flow through a full vertical section of aquifer 1 m wide under unit hydraulic gradient. High T → well yields high discharge. Used in: Thiem equation (confined steady-state), Theis equation (transient), Jacob straight-line method.
- 27Fluid MechanicsHARD
The 'Dupuit-Forchheimer assumptions' for unconfined aquifer flow include:
AFlow is always vertical onlyBFlow is horizontal; velocity proportional to water table slope dh/dx (not actual angle) — valid for gentle water table gradientsCSoil is isotropic and impermeableDNo groundwater exists in unconfined aquiferAnswer: B. Flow is horizontal; velocity proportional to water table slope dh/dx (not actual angle) — valid for gentle water table gradients
Explanation: Dupuit assumptions: (1) Flow is horizontal (streamlines are horizontal in unconfined aquifer); (2) Velocity gradient is proportional to slope of water table dh/dx at that point (not to angle). These simplify to: q = −kh(dh/dx). Valid for mild water table slopes (< 1:10). Breaks down near wells (steep gradients) and at seepage faces. Gives parabolic water table between drains.
- 28Fluid MechanicsMEDIUM
'Cavitation' in centrifugal pumps occurs when:
ADischarge pressure is too highBLocal suction pressure drops below vapour pressure — bubbles form and collapse causing pitting and vibrationCPump is running too slowlyDDischarge pipe is too shortAnswer: B. Local suction pressure drops below vapour pressure — bubbles form and collapse causing pitting and vibration
Explanation: Cavitation: local pressure drops below vapour pressure → vapour bubbles form → collapse violently on high-pressure side → pitting, vibration, noise, efficiency loss. Prevented by: ensuring NPSH_available > NPSH_required. NPSH_a = (pa−pv)/γ + Hs − hL (atmospheric, vapour, suction head, losses). Cavitation likely when: pump set too high above sump, long suction line, hot liquid, high altitude.
- 29Fluid MechanicsHARD
The 'gradually varied flow' (GVF) equation in open channels is derived from:
AContinuity equation aloneBEnergy equation for non-uniform flow: dy/dx = (So−Sf)/(1−Fr²) — slope of water surface depends on bed slope, friction, and FrCBernoulli equation between two fixed pointsDMomentum equation ignoring frictionAnswer: B. Energy equation for non-uniform flow: dy/dx = (So−Sf)/(1−Fr²) — slope of water surface depends on bed slope, friction, and Fr
Explanation: GVF equation: dy/dx = (So − Sf)/(1 − Fr²) where So = bed slope, Sf = friction slope (energy gradient), Fr = Froude number = V/√(gD). Derived from energy equation for non-uniform flow. If So > Sf and Fr < 1: backwater curve (M1 or S1); if So < Sf: drawdown. Critical depth occurs at Fr=1. Numerical integration (standard step method or direct step method) solves GVF profile.
- 30Fluid MechanicsMEDIUM
The 'specific speed' Ns of a turbine is defined as the speed of a geometrically similar turbine that:
AProduces 1 kW under 1 m headBGeometric similar turbine that produces unit power under unit head at unit speed — used for type classification (Pelton/Francis/Kaplan)CRotates at 1 rpmDHas the highest efficiencyAnswer: B. Geometric similar turbine that produces unit power under unit head at unit speed — used for type classification (Pelton/Francis/Kaplan)
Explanation: Specific speed Ns = N√P / H^(5/4) (power form) or Ns = N√Q / H^(3/4) (flow form). Represents the speed at which a geometrically similar (but unit-sized) turbine would produce unit power under unit head. Type selection: Pelton Ns < 60; Francis 60–300; Kaplan 300–900. Ns is NOT specific to a size — it is a dimensionless similarity parameter for turbine type classification.
- 31Fluid Mechanics and HydraulicsEASY
Manning's formula is used for:
ABending stressBConsolidation settlementCSoil classificationDUniform open channel flowAnswer: D. Uniform open channel flow
Explanation: Manning equation estimates velocity in open channels using roughness, hydraulic radius and slope.
- 32Fluid Mechanics and HydraulicsHARD
For a pump delivering 0.05 m3/s against 20 m head with efficiency 80 percent, input power is nearly:
A12.26 kWB15.70 kWC9.81 kWD7.85 kWAnswer: A. 12.26 kW
Explanation: Input power = gamma QH/eta = 9.81 x 0.05 x 20/0.8 = 12.26 kW.
- 33Hydraulic Radius Max FlowMEDIUM
For maximum discharge in a circular pipe flowing partly full (not full), the depth of flow that gives maximum discharge is approximately:
A0.5D (half full)B0.81DC0.94DDFull (D)Answer: C. 0.94D
Explanation: For a circular pipe, maximum discharge occurs at depth = 0.94D (94% full), not when completely full. This is because at 0.94D, the product A x R^(2/3) is maximum. At full flow, the increased wetted perimeter reduces velocity enough to lower Q.
- 34Dimensional AnalysisMEDIUM
In Buckingham pi theorem, if a physical problem involves n variables and m fundamental dimensions, the number of independent dimensionless pi groups is:
An + mBn - mCn x mDm / nAnswer: B. n - m
Explanation: Buckingham pi theorem: number of pi groups = n - m, where n = total number of variables and m = number of fundamental dimensions (M, L, T for most fluid mechanics problems).
- 35Surface TensionMEDIUM
The rise of liquid in a capillary tube of radius r (surface tension sigma, contact angle theta) is given by:
Ah = 2 sigma cos(theta) / (rho g r)Bh = sigma / (rho g r)Ch = rho g r / sigmaDh = 2 r sigma / gAnswer: A. h = 2 sigma cos(theta) / (rho g r)
Explanation: Capillary rise: h = 2 sigma cos(theta) / (rho x g x r). For water in glass (theta = 0): h = 2 sigma / (rho x g x r). Capillary rise is significant in small tubes and fine-grained soils.
- 36Manning EquationMEDIUM
Manning equation for open channel flow: V = (1/n) x R^(2/3) x S^(1/2). For a circular pipe flowing full, the hydraulic radius R equals:
ADBD/4CD/2Dpi x D/4Answer: B. D/4
Explanation: For a full circular pipe of diameter D: A = pi x D2/4, P (wetted perimeter) = pi x D, R = A/P = D/4. So Manning: V = (1/n) x (D/4)^(2/3) x S^(1/2).
- 37Hydraulic GradientMEDIUM
The hydraulic grade line (HGL) in pipe flow lies below the energy grade line (EGL) by a distance equal to:
AThe head loss due to frictionBThe pressure head at that sectionCThe velocity head V2/2gDThe elevation head zAnswer: C. The velocity head V2/2g
Explanation: EGL = HGL + V2/2g. The HGL is at the piezometric head (p/gamma + z), and EGL includes the velocity head. So EGL - HGL = V2/2g at any section.
- 38Fluid Mechanics and HydraulicsHARD
The most economical trapezoidal channel section has hydraulic radius equal to:
Ay/4By/2Cy/3DyAnswer: B. y/2
Explanation: For the best hydraulic trapezoidal section, hydraulic radius R = y/2, as in the best rectangular section.
- 39Fluid Mechanics and HydraulicsHARD
The momentum correction factor beta for laminar pipe flow is:
A2.0B1.0C1.33D4.0Answer: C. 1.33
Explanation: For laminar pipe flow, beta = 4/3; turbulent flow is nearer to 1.
- 40Fluid Mechanics and HydraulicsHARD
The kinetic energy correction factor alpha for laminar pipe flow is:
A1.0B2.0C1.33D3.0Answer: B. 2.0
Explanation: For parabolic laminar velocity distribution in a circular pipe, alpha = 2; for turbulent flow it is close to 1.
- 41Fluid Mechanics and HydraulicsHARD
The pressure intensity at a depth h below a free liquid surface is:
Ah/gammaBrho/gCgamma/hDgamma hAnswer: D. gamma h
Explanation: Hydrostatic pressure increases linearly with depth: p = gamma h.
- 42Fluid Mechanics and HydraulicsHARD
For laminar flow through a circular pipe, the Darcy-Weisbach friction factor is:
A64/ReB16/ReC32/ReD0.316/Re^0.25Answer: A. 64/Re
Explanation: Using Darcy friction factor convention, f = 64/Re for fully developed laminar pipe flow.
- 43Hydraulics, Hydrology and IrrigationMEDIUM
A centrifugal pump converts mechanical energy into pressure energy through impeller action.
Aimpeller action increasing headBrail sleeper actionCsoil shearDfilter media onlyAnswer: A. impeller action increasing head
Explanation: Centrifugal pumps add energy to fluid using a rotating impeller.
- 44Hydraulics, Hydrology and IrrigationEASY
Command area is the area that can be irrigated by a canal system.
Abridge deck areaBriver catchment onlyCirrigable area under commandDurban road areaAnswer: C. irrigable area under command
Explanation: Command is the area served by irrigation.
- 45Hydraulics, Hydrology and IrrigationEASY
The standard meaning of canal head regulator is:
Acuts reinforcementBmeasures rainfallCregulates entry of water from river into canalDsupports bridge deckAnswer: C. regulates entry of water from river into canal
Explanation: regulates entry of water from river into canal is the correct association for canal head regulator.
- 46Hydraulics, Hydrology and IrrigationMEDIUM
In standard practice, open channel flow indicates:
Aflow only in soil voidsBflow with free surface exposed to atmosphereCflow without gravityDflow in a full pressure pipeAnswer: B. flow with free surface exposed to atmosphere
Explanation: flow with free surface exposed to atmosphere is the correct association for open channel flow.
- 47Hydraulics, Hydrology and IrrigationEASY
Warabandi is rotational water distribution among farmers.
Apavement designBpump testingCrotational distributionDsoil gradingAnswer: C. rotational distribution
Explanation: Warabandi schedules equitable canal water supply.
- 48Fluid Mechanics and HydraulicsMEDIUM
Total pressure on a vertical plane surface submerged in liquid acts at:
ACentroid alwaysBFree surfaceCCentre of pressureDMetacentreAnswer: C. Centre of pressure
Explanation: Resultant hydrostatic force acts through centre of pressure below centroid.
- 49Fluid Mechanics and HydraulicsHARD
Pressure head corresponding to 49.05 kPa water pressure is:
A5 mB2.5 mC49 mD10 mAnswer: A. 5 m
Explanation: Head = p/gamma = 49.05/9.81 = 5 m of water.
- 50Fluid Mechanics and HydraulicsMEDIUM
Flow is rotational when:
AVelocity is zero everywhereBDensity is constantCPressure is uniform onlyDFluid particles have angular velocityAnswer: D. Fluid particles have angular velocity
Explanation: Rotational flow has nonzero vorticity.