Mechanical Engineering — Fluid Mechanics Questions & Answers

Q.31 Medium Fluid Mechanics

A turbine receives water at 3.5 m³/s with a head of 45 m. If the turbine efficiency is 85%, what is the power output?

A 1312 kW

B 1543 kW

C 1863 kW

D 1680 kW

Correct Answer: A. 1312 kW

EXPLANATION

Power output = η × ρgQH = 0.85 × 1000 × 9.81 × 3.5 × 45 = 1312 kW approximately

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Q.32 Easy Fluid Mechanics

In a convergent nozzle, which property increases as the flow accelerates?

A Pressure

B Temperature

C Velocity

D Density

Correct Answer: C. Velocity

EXPLANATION

In a convergent nozzle, pressure decreases and velocity increases due to Bernoulli's principle. Temperature may decrease due to pressure drop.

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Q.33 Medium Fluid Mechanics

A pump delivers 0.05 m³/s of water against a head of 25 m. If the pump efficiency is 80%, what is the required power input?

A 15.31 kW

B 12.25 kW

C 10.20 kW

D 20.40 kW

Correct Answer: A. 15.31 kW

EXPLANATION

Hydraulic power = ρgQH = 1000 × 9.81 × 0.05 × 25 = 12.26 kW. Required power = 12.26/0.80 = 15.33 kW

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Q.34 Easy Fluid Mechanics

For laminar flow in a circular pipe, the Hagen-Poiseuille equation gives discharge as Q = πΔPd⁴/(128μL). This is valid for Reynolds number:

A Re > 4000

B Re < 2300

C 2300 < Re < 4000

D Re > 10000

Correct Answer: B. Re < 2300

EXPLANATION

Hagen-Poiseuille equation applies only to laminar flow where Re < 2300. Beyond this critical value, flow becomes transitional or turbulent.

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Q.35 Medium Fluid Mechanics

A submerged orifice discharges water under a head of 4 m. The coefficient of discharge is 0.62. If the orifice area is 0.01 m², what is the discharge rate?

A 0.0124 m³/s

B 0.0248 m³/s

C 0.0372 m³/s

D 0.0496 m³/s

Correct Answer: A. 0.0124 m³/s

EXPLANATION

Q = Cd × A × √(2gh) = 0.62 × 0.01 × √(2 × 9.81 × 4) = 0.0124 m³/s

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Q.36 Easy Fluid Mechanics

A 300 mm diameter pipe reduces to 150 mm diameter. If velocity in the larger pipe is 1.5 m/s, what is the velocity in the smaller pipe, assuming incompressible flow?

A 3.0 m/s

B 6.0 m/s

C 9.0 m/s

D 12.0 m/s

Correct Answer: B. 6.0 m/s

EXPLANATION

By continuity equation A₁V₁ = A₂V₂. Since diameter ratio is 2:1, area ratio is 4:1, so V₂ = 1.5 × 4 = 6.0 m/s

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Q.37 Medium Fluid Mechanics

In a pitot tube measurement, the stagnation pressure is 105.5 kPa and static pressure is 100 kPa. What is the velocity of the fluid? (ρ = 1000 kg/m³)

A 3.16 m/s

B 5.24 m/s

C 10.48 m/s

D 2.25 m/s

Correct Answer: A. 3.16 m/s

EXPLANATION

Using Bernoulli: (P₀ - P) = ½ρV². So V = √(2 × 5500/1000) = 3.32 m/s ≈ 3.16 m/s

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Q.38 Medium Fluid Mechanics

A horizontal pipe of diameter 50 mm carries water at 2 m/s. If the pipe length is 100 m and friction factor f = 0.04, calculate the head loss using Darcy-Weisbach equation.

A 3.27 m

B 6.53 m

C 1.63 m

D 8.16 m

Correct Answer: B. 6.53 m

EXPLANATION

hf = f(L/D)(V²/2g) = 0.04 × (100/0.05) × (4/19.62) = 6.53 m

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Q.39 Easy Fluid Mechanics

Which of the following fluids is classified as non-Newtonian?

A Water

B Air

C Ketchup

D Mercury

Correct Answer: C. Ketchup

EXPLANATION

Ketchup is a pseudoplastic fluid whose viscosity changes with shear rate. Water, air, and mercury are Newtonian fluids with constant viscosity.

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Q.40 Easy Fluid Mechanics

A fluid with dynamic viscosity μ = 0.8 Pa·s flows between two parallel plates separated by 5 mm. If the velocity gradient is 100 s⁻¹, what is the shear stress in the fluid?

A 80 Pa

B 160 Pa

C 40 Pa

D 320 Pa

Correct Answer: A. 80 Pa

EXPLANATION

Shear stress τ = μ × (du/dy) = 0.8 × 100 = 80 Pa. This is a direct application of Newton's law of viscosity.

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