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Question 1 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines The SI unit of kinematic viscosity is
Choose your answer for question 1 A. N/m² B. kg/m·s C. N·s/m² D. m²/sAnswer and explanation Correct answer: D
ν = μ/ρ, so its unit is m²/s. N·s/m² is the unit of dynamic viscosity.
Question 2 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines A difference of 100 mm of mercury (density 13 600 kg/m³) corresponds to a pressure difference of about
Choose your answer for question 2 A. 13.3 kPa B. 133 kPa C. 0.98 kPa D. 9.81 kPaAnswer and explanation Correct answer: A
Δp = ρgh = 13 600 × 9.81 × 0.1 = 13 342 Pa ≈ 13.3 kPa.
Question 3 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines A Pitot tube is used to measure
Choose your answer for question 3 A. the density of a fluid B. the viscosity of a fluid C. the surface tension D. the local velocity of flowAnswer and explanation Correct answer: D
It senses the stagnation pressure, and with the static pressure gives the velocity head.
Question 4 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines The Reynolds number is the ratio of
Choose your answer for question 4 A. viscous forces to inertial forces B. inertial forces to viscous forces C. pressure forces to surface tension forces D. gravity forces to inertial forcesAnswer and explanation Correct answer: B
Re = ρVD/μ. It decides whether flow is laminar or turbulent.
Question 5 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines Cavitation in a pump occurs when the pressure at some point in the liquid falls below
Choose your answer for question 5 A. the atmospheric pressure B. the delivery pressure C. the vapour pressure of the liquid at that temperature D. the critical pressureAnswer and explanation Correct answer: C
Vapour bubbles form and later collapse violently on reaching higher pressure, causing noise, vibration and pitting.
Question 6 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines A Kaplan turbine is
Choose your answer for question 6 A. an impulse turbine for high heads B. a radial flow turbine for very high heads C. a tangential flow turbine D. an axial flow reaction turbine for low headsAnswer and explanation Correct answer: D
The Kaplan runner has adjustable blades and suits large discharges at low heads.
Question 7 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines The overall efficiency of a centrifugal pump is the product of
Choose your answer for question 7 A. mechanical and thermal efficiencies B. volumetric and thermal efficiencies C. hydraulic and thermal efficiencies D. hydraulic, mechanical and volumetric efficienciesAnswer and explanation Correct answer: D
η = ηh × ηm × ηv, covering the losses in the flow passages, the bearings and the leakage.
Question 8 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines An air vessel is fitted to a reciprocating pump to
Choose your answer for question 8 A. cool the cylinder B. prime the pump C. obtain a uniform discharge and reduce friction and acceleration head D. increase the suction liftAnswer and explanation Correct answer: C
The vessel absorbs surges of flow, so a steadier stream flows in the pipe and the pump can run at higher speed.
Question 9 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines In a hydraulic press, the small piston has an area of 10 cm² and the large piston 500 cm². A force of 200 N on the small piston produces a force on the large piston of
Choose your answer for question 9 A. 100 kN B. 10 kN C. 1 kN D. 4 kNAnswer and explanation Correct answer: B
Pressure is the same on both pistons: F2 = F1 × (A2/A1) = 200 × 50 = 10 000 N.
Question 10 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines In the Buckingham π theorem, if there are n variables and m fundamental dimensions, the number of dimensionless groups is
Choose your answer for question 10 A. n + m B. n − m C. n × m D. m − nAnswer and explanation Correct answer: B
The variables are reduced to (n − m) independent dimensionless π terms.
Question 11 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines Separation of the boundary layer from a surface takes place because of
Choose your answer for question 11 A. a high free stream velocity only B. zero velocity at the free stream C. a favourable pressure gradient D. an adverse pressure gradientAnswer and explanation Correct answer: D
When the pressure rises in the flow direction, the fluid near the wall loses momentum and the flow reverses.
Question 12 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines The draft tube of a reaction turbine
Choose your answer for question 12 A. converts kinetic energy of the exit water into pressure and lets the runner be set above the tail water B. works as a governor C. increases the speed of the runner D. reduces the dischargeAnswer and explanation Correct answer: A
A gradually widening tube recovers energy and keeps the runner exit pressure below atmospheric, adding to the effective head.
Question 13 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines Air of density 1.2 kg/m³ flows at 10 m/s through a duct of area 0.01 m². The mass flow rate is
Choose your answer for question 13 A. 0.12 kg/s B. 0.012 kg/s C. 12 kg/s D. 1.2 kg/sAnswer and explanation Correct answer: A
ṁ = ρAV = 1.2 × 0.01 × 10 = 0.12 kg/s.
Question 14 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines The flow of a gas is supersonic when the Mach number is
Choose your answer for question 14 A. less than 1 B. greater than 1 C. equal to 0 D. equal to 0.5Answer and explanation Correct answer: B
Mach number M = V/c, where c is the speed of sound. M = 1 is sonic flow.
Question 15 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines A Pitot-static tube in air (ρ = 1.2 kg/m³) reads a pressure difference of 1.8 kPa between the stagnation and static pressures. The air velocity is
Choose your answer for question 15 A. 54.8 m/s B. 77.5 m/s C. 27.4 m/s D. 38.7 m/sAnswer and explanation Correct answer: A
v = √(2Δp/ρ) = √(2 × 1800 / 1.2) = √3000 = 54.8 m/s.
Question 16 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines In fully developed laminar flow in a circular pipe, the maximum velocity is
Choose your answer for question 16 A. twice the mean velocity B. 1.5 times the mean velocity C. equal to the mean velocity D. three times the mean velocityAnswer and explanation Correct answer: A
The parabolic profile has umax = 2 × the average velocity.
Question 17 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines For laminar flow in a pipe at a Reynolds number of 1600, the Darcy friction factor is
Choose your answer for question 17 A. 0.004 B. 0.02 C. 0.4 D. 0.04Answer and explanation Correct answer: D
f = 64/Re = 64/1600 = 0.04.
Question 18 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines A pump delivers 0.05 m³/s of water against a head of 20 m with an overall efficiency of 70 percent. The input power is about
Choose your answer for question 18 A. 9.81 kW B. 7.0 kW C. 14.0 kW D. 19.6 kWAnswer and explanation Correct answer: C
Hydraulic power = ρgQH = 9810 × 0.05 × 20 = 9.81 kW. Input = 9.81/0.7 = 14.0 kW.
Question 19 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines The specific speed of a hydraulic turbine, in terms of the speed N, power P and head H, is
Choose your answer for question 19 A. N√Q / H^(3/4) B. N√P / H^(3/4) C. N P / H² D. N√P / H^(5/4)Answer and explanation Correct answer: D
For turbines Ns = N√P / H^(5/4). The expression N√Q / H^(3/4) is the specific speed of a pump.
Question 20 · Mechanical Engineering (SSC JE) · Fluid Mechanics and Machines If the speed of a centrifugal pump is doubled, the head produced (by the affinity laws) becomes
Choose your answer for question 20 A. 2 times B. 16 times C. 8 times D. 4 timesAnswer and explanation Correct answer: D
H ∝ N² D², so doubling N makes H four times, Q twice and power eight times.