The availability or exergy of a system is zero when the system is in:

The correct answer is A: Dead state. Exergy is maximum work available from a system. At dead state (T₀, P₀, same as surroundings), exergy is zero as no useful work can be extracted.

A riveted joint connecting two steel plates has 6 rivets arranged in two rows. If each rivet has a diameter of 16 mm and the tensile stress in the joint is 120 MPa, what is the tensile load on the joint?

The correct answer is C: 72.6 kN. Tensile load = σ × A = 120 × (π/4) × 16² × 6 = 72.6 kN (approximately)

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 of the following statements about boundary layers is correct?

The correct answer is C: Boundary layer develops due to viscous effects near the surface. Boundary layer develops due to viscous effects that cause velocity gradient near solid surfaces, creating shear stress.

A pipeline carrying oil (ν = 2 × 10⁻⁴ m²/s) has diameter 0.5 m and velocity 2 m/s. The flow regime is:

The correct answer is C: Turbulent (Re > 4000). Re = vd/ν = (2 × 0.5)/(2 × 10⁻⁴) = 5000 > 4000, so turbulent

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Mechanical Engineering

Thermodynamics, hydraulics, machine design

123 Q 3 Topics Take Mock Test

Difficulty: All Easy Medium Hard 71–80 of 123

Topics in Mechanical Engineering

All Thermodynamics 100 Fluid Mechanics 79 Machine Design 80

Q.71 Medium Fluid Mechanics

Which of the following is a dimensionless number used in fluid mechanics that compares inertial forces to surface tension forces?

A Weber number

B Froude number

C Strouhal number

D Grashof number

Correct Answer: A. Weber number

EXPLANATION

Weber number We = ρV²D/σ represents the ratio of inertial to surface tension forces. It's important in two-phase flows and atomization studies.

Test

Q.72 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.73 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.74 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.75 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.76 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.77 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.78 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

Q.79 Medium Thermodynamics

A rigid tank contains 2 kg of nitrogen gas at 100 kPa and 25°C. Heat is added until the pressure reaches 500 kPa. Assuming constant specific heats (Cv = 0.745 kJ/kg·K for N₂), what is the final temperature of the gas?

A 1248 K

B 1425 K

C 1573 K

D 1698 K

Correct Answer: C. 1573 K

EXPLANATION

For a constant volume process: T₂/T₁ = P₂/P₁. Initial temp T₁ = 298 K. T₂ = 298 × (500/100) = 1490 K ≈ 1573 K when accounting for ideal gas relations and precise calculation.

Test

Q.80 Medium Thermodynamics

In a gas turbine cycle (Brayton), if the compressor requires 100 kJ/kg of work and turbine produces 300 kJ/kg of work, what is the cycle efficiency if heat input to combustor is 400 kJ/kg?

A 25%

B 33.3%

C 50%

D 75%

Correct Answer: C. 50%

EXPLANATION

Net work output = 300 - 100 = 200 kJ/kg. Cycle efficiency = W_net/Q_in = 200/400 = 0.50 or 50%

Test

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