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Question 1 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics The gauge pressure at a depth of 10 m in still water is approximately (g = 9.81 m/s²)
Choose your answer for question 1 A. 981 kPa B. 10 kPa C. 98.1 kPa D. 9.81 kPaAnswer and explanation Correct answer: C
p = ρgh = 1000 × 9.81 × 10 = 98 100 Pa = 98.1 kPa.
Question 2 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics Flow in a circular pipe is generally laminar when the Reynolds number is below about
Choose your answer for question 2 A. 10000 B. 4000 C. 2000 D. 500Answer and explanation Correct answer: C
Flow is laminar for Re < 2000, transitional between about 2000 and 4000, and turbulent beyond that.
Question 3 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics Bernoulli’s equation for steady, incompressible, non-viscous flow is a statement of the conservation of
Choose your answer for question 3 A. energy B. momentum C. mass D. angular momentumAnswer and explanation Correct answer: A
The sum of pressure head, velocity head and datum head stays constant along a streamline, which expresses energy conservation.
Question 4 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics Water flows at 2 m/s in a pipe of 20 cm diameter that reduces to 10 cm diameter. The velocity in the smaller section is
Choose your answer for question 4 A. 4 m/s B. 16 m/s C. 8 m/s D. 2 m/sAnswer and explanation Correct answer: C
A1V1 = A2V2. Area is proportional to d², so V2 = 2 × (20/10)² = 8 m/s.
Question 5 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics The discharge over a right-angled triangular notch varies with the head H as
Choose your answer for question 5 A. H^(3/2) B. H² C. H^(1/2) D. H^(5/2)Answer and explanation Correct answer: D
For a V-notch Q = (8/15) Cd √(2g) tan(θ/2) H^(5/2). A rectangular notch varies as H^(3/2).
Question 6 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics A hydraulic jump occurs when the flow changes from
Choose your answer for question 6 A. subcritical to supercritical B. uniform to critical C. supercritical to subcritical D. laminar to turbulentAnswer and explanation Correct answer: C
A jump forms when a fast, shallow (supercritical) stream meets a slower, deeper (subcritical) one, with energy loss and a rise in depth.
Question 7 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics In Manning’s formula, the mean velocity of flow is proportional to the hydraulic radius R raised to the power
Choose your answer for question 7 A. 2/3 B. 1/2 C. 3/2 D. 1/3Answer and explanation Correct answer: A
Manning’s formula is V = (1/n) R^(2/3) S^(1/2).
Question 8 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics For the most economical rectangular channel section, the depth of flow is
Choose your answer for question 8 A. equal to the bottom width B. twice the bottom width C. one-third of the bottom width D. half of the bottom widthAnswer and explanation Correct answer: D
For a rectangle the best hydraulic section has b = 2y, and then R = y/2.
Question 9 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics A venturimeter is used to measure
Choose your answer for question 9 A. the viscosity of a liquid B. the pressure in a tank C. the rate of flow (discharge) in a pipe D. the depth of flow in an open channelAnswer and explanation Correct answer: C
It uses the pressure drop between the inlet and the throat of a converging-diverging pipe section to find the discharge.
Question 10 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics The theoretical velocity of efflux from a small orifice under a constant head of 5 m (g = 9.81 m/s²) is
Choose your answer for question 10 A. 49.0 m/s B. 4.95 m/s C. 9.9 m/s D. 7.0 m/sAnswer and explanation Correct answer: C
Torricelli’s theorem gives v = √(2gh) = √(2 × 9.81 × 5) = √98.1 = 9.9 m/s.
Question 11 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics A vertical rectangular gate 2 m wide and 3 m deep has its top edge level with the free water surface. The total hydrostatic force on it is (γ = 9.81 kN/m³)
Choose your answer for question 11 A. 58.86 kN B. 176.58 kN C. 88.29 kN D. 29.43 kNAnswer and explanation Correct answer: C
F = γ A h̄ = 9.81 × (2 × 3) × 1.5 = 88.29 kN.
Question 12 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics The centre of pressure on a vertical rectangular plate with its top edge at the free surface lies below the surface at
Choose your answer for question 12 A. 1/2 of the depth B. 2/3 of the depth C. 3/4 of the depth D. 1/3 of the depthAnswer and explanation Correct answer: B
h* = h̄ + I/(A h̄) = d/2 + (bd³/12)/(bd × d/2) = d/2 + d/6 = 2d/3.
Question 13 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics A floating body is in stable equilibrium if its metacentre lies
Choose your answer for question 13 A. below the centre of gravity B. at the centre of buoyancy C. below the centre of buoyancy D. above the centre of gravityAnswer and explanation Correct answer: D
A positive metacentric height (GM > 0) gives a restoring couple when the body is tilted.
Question 14 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics Water flows at 2 m/s through a 100 mm diameter pipe 100 m long with a friction factor f = 0.02. The head loss by the Darcy-Weisbach equation is about
Choose your answer for question 14 A. 2.04 m B. 4.08 m C. 8.0 m D. 0.41 mAnswer and explanation Correct answer: B
hf = f L V² / (2 g d) = 0.02 × 100 × 4 / (2 × 9.81 × 0.1) = 8 / 1.962 ≈ 4.08 m.
Question 15 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics The hydraulic grade line represents the sum of
Choose your answer for question 15 A. the pressure head and the datum head B. the total energy of the flow C. the velocity head and the datum head D. the pressure head and the velocity head onlyAnswer and explanation Correct answer: A
The HGL is the piezometric level. The energy grade line is higher than it by the velocity head V²/2g.
Question 16 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics A centrifugal pump must be primed before starting in order to
Choose your answer for question 16 A. increase the speed of the motor B. reduce the discharge C. cool the bearings D. remove air from the casing and the suction pipeAnswer and explanation Correct answer: D
A pump full of air cannot create enough suction to lift water, since air is far lighter than water.
Question 17 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics A Pelton wheel is an impulse turbine most suitable for
Choose your answer for question 17 A. very low head and very high discharge B. medium head and any discharge only C. low head and high discharge D. high head and low dischargeAnswer and explanation Correct answer: D
Water jets strike the buckets at atmospheric pressure, which suits mountain sites with a high head.
Question 18 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics For a Newtonian fluid, the shear stress is proportional to
Choose your answer for question 18 A. the velocity gradient (rate of shear strain) B. the velocity C. the pressure D. the densityAnswer and explanation Correct answer: A
Newton’s law of viscosity is τ = μ du/dy, where μ is the dynamic viscosity.
Question 19 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics Flow in a circular pipe has a Reynolds number of 33614. The flow is
Choose your answer for question 19 A. turbulent B. in the transition range C. supersonic D. laminarAnswer and explanation Correct answer: A
Flow in a pipe is laminar for Re < 2000, turbulent for Re > 4000, and in the transition range between them. 33614 falls in the turbulent range.
Question 20 · Civil Engineering (SSC JE) · Fluid Mechanics and Hydraulics A block of density 900 kg/m³ floats in water. The fraction of its volume submerged is
Choose your answer for question 20 A. 1.111 B. 0.45 C. 0.9 D. 0.1Answer and explanation Correct answer: C
Submerged fraction = ρbody/ρfluid = 900/1000 = 0.9.