What is the significance of the 'Hertzian stress' in rolling contact bearings?

The correct answer is B: It is the maximum compressive stress occurring at the contact surface. Hertzian contact stress is the maximum compressive stress that occurs at the contact surface between rolling elements and raceways, critical for fatigue analysis.

Which of the following processes has zero work done by/on the gas?

The correct answer is B: Isochoric (constant volume) process. Work W = ∫P dV. In isochoric process, dV = 0, therefore W = 0 regardless of pressure or temperature changes.

For a real gas undergoing Joule-Thomson expansion through a throttle valve, the Joule-Thomson coefficient (μ_JT) is negative. This means:

The correct answer is A: Temperature increases during expansion. μ_JT = (∂T/∂P)_H. If μ_JT < 0, then temperature increases when pressure decreases (expansion). Negative μ_JT occurs above inversion temperature.

For an ideal gas undergoing an isothermal process, the change in internal energy is:

The correct answer is B: Zero. In an isothermal process, temperature is constant. For an ideal gas, internal energy depends only on temperature, so ΔU = 0.

Which dimensionless number is used to characterize the relative importance of gravity and inertial forces in open channel flow?

The correct answer is B: Froude number. The Froude number Fr = V/√(gD_h) characterizes gravity effects. In open channel flow, it determines flow regime (subcritical Fr1).

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Mechanical Engineering
Fluid Mechanics

Thermodynamics, hydraulics, machine design

37 Q 3 Topics Take Mock Test

Difficulty: All Easy Medium Hard 31–37 of 37

Topics in Mechanical Engineering

All Thermodynamics 100 Fluid Mechanics 79 Machine Design 80

Q.31 Medium Fluid Mechanics

The Reynolds number for flow in a circular pipe is given by Re = ρVD/μ. If the flow transitions from laminar to turbulent at Re ≈ 2300, then for a pipe with D = 0.025 m and V = 1.5 m/s (ρ = 1000 kg/m³, μ = 0.001 N·s/m²), the flow regime is:

A Definitely laminar

B Definitely turbulent

C In transition zone

D Cannot be determined

Correct Answer: B. Definitely turbulent

EXPLANATION

Re = (1000 × 1.5 × 0.025)/0.001 = 37,500, which is much greater than 2300, indicating turbulent flow.

Test

Q.32 Medium Fluid Mechanics

A fluid element has shear stress τ = 0.5 Pa and velocity gradient du/dy = 10 s⁻¹. The dynamic viscosity of the fluid is:

A 0.05 N·s/m²

B 0.005 N·s/m²

C 0.5 N·s/m²

D 5.0 N·s/m²

Correct Answer: A. 0.05 N·s/m²

EXPLANATION

From Newton's law of viscosity, τ = μ(du/dy), so μ = τ/(du/dy) = 0.5/10 = 0.05 N·s/m²

Test

Q.33 Medium Fluid Mechanics

For turbulent flow in pipes, the Colebrook-White equation is used to find the friction factor. Which of the following is NOT an input parameter?

A Reynolds number

B Relative roughness

C Mach number

D Diameter of pipe

Correct Answer: C. Mach number

EXPLANATION

The Colebrook-White equation involves Reynolds number and relative roughness but not Mach number. Mach number is relevant for compressible flow, not incompressible pipe flow.

Test

Q.34 Medium Fluid Mechanics

The Mach number is the ratio of:

A Inertia force to viscous force

B Velocity of flow to velocity of sound

C Pressure force to inertia force

D Kinetic energy to potential energy

Correct Answer: B. Velocity of flow to velocity of sound

EXPLANATION

Mach number M = V/a, where V is flow velocity and a is the speed of sound. It indicates whether flow is subsonic (M<1), sonic (M=1), or supersonic (M>1).

Test

Q.35 Medium Fluid Mechanics

Water flows through a horizontal pipe with diameter 0.05 m at a velocity of 2 m/s. The volumetric flow rate is:

A 0.00393 m³/s

B 0.00785 m³/s

C 0.0157 m³/s

D 0.0314 m³/s

Correct Answer: A. 0.00393 m³/s

EXPLANATION

Q = AV = (π/4)D² × V = (π/4) × 0.05² × 2 = 0.00393 m³/s

Test

Q.36 Medium Fluid Mechanics

The Darcy friction factor for fully developed laminar flow in a pipe depends on:

A Relative roughness only

B Reynolds number only

C Both Reynolds number and relative roughness

D Neither Reynolds number nor roughness

Correct Answer: B. Reynolds number only

EXPLANATION

For laminar flow, friction factor f = 64/Re is independent of surface roughness. Roughness effects become significant only in turbulent flow.

Test

Q.37 Medium Fluid Mechanics

A pump delivers 0.05 m³/s of water. If the pipe diameter is 0.1 m, the velocity of flow is:

A 6.37 m/s

B 5.09 m/s

C 3.18 m/s

D 12.74 m/s

Correct Answer: A. 6.37 m/s

EXPLANATION

Using Q = AV = (π/4)D²V, we get V = Q/A = 0.05/(π/4 × 0.1²) = 0.05/0.00785 = 6.37 m/s

Test

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