In a throttling process (Joule-Thomson expansion), the enthalpy of the fluid:

The correct answer is C: Remains constant. Throttling is an isenthalpic process where enthalpy remains constant (H_initial = H_final) as the fluid expands through a restriction.

A reversible adiabatic process for an ideal gas is also known as:

The correct answer is C: Isentropic process. A reversible adiabatic process has constant entropy (dS = 0), making it isentropic. This is a key assumption in many thermodynamic analysis for ideal processes.

For a submerged curved vane deflecting a jet, the component of force in the direction of jet is:

The correct answer is B: ρQv(1 - cos θ). Force component = ρQv(1 - cos θ) where θ is deflection angle from momentum equation.

The Mach number M = 0.3 indicates:

The correct answer is B: Incompressible flow assumption is valid. M < 0.3 indicates incompressible flow approximation is valid; compressibility effects are negligible.

Which of the following statements is TRUE regarding stress concentration in machine design?

The correct answer is C: Stress concentration is more critical at lower speeds. At lower speeds (static loading), stress concentration has more severe effects as fatigue is not a factor and stress peaks can cause immediate failure. Larger fillet radii reduce stress concentration.

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Mechanical Engineering
Fluid Mechanics

Thermodynamics, hydraulics, machine design

79 Q 3 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 79

Topics in Mechanical Engineering

All Thermodynamics 100 Fluid Mechanics 79 Machine Design 80

Q.1 Hard Fluid Mechanics

The cavitation parameter σ = (P - Pv)/(0.5ρV²) indicates the tendency of a flowing fluid to cavitate. Cavitation occurs when σ drops below a critical value σc. For a given pump, lowering the inlet pressure or raising the fluid temperature will:

A Increase σ and reduce cavitation risk

B Decrease σ and increase cavitation risk

C Keep σ constant

D Increase Pv but not affect cavitation

Correct Answer: B. Decrease σ and increase cavitation risk

EXPLANATION

Lowering inlet pressure decreases (P - Pv), reducing σ. Raising temperature increases Pv, also reducing σ. Both conditions increase cavitation risk in turbomachinery. This is critical in high-speed pump operations.

Test

Q.2 Easy Fluid Mechanics

In centrifugal pump design, the impeller exit diameter D₂ and speed N (rpm) determine the peripheral velocity U₂ = πD₂N/60. For a pump with D₂ = 300 mm running at 1500 rpm, the peripheral velocity is:

A 23.56 m/s

B 28.45 m/s

C 35.62 m/s

D 42.78 m/s

Correct Answer: A. 23.56 m/s

EXPLANATION

U₂ = π × 0.3 × 1500/60 = 23.56 m/s. This velocity is critical in pump design as it affects the Euler's head and pump efficiency in Indian water supply and irrigation projects.

Test

Q.3 Medium Fluid Mechanics

The Froude number Fr = V/√(gD) for channel flow determines the flow type. For Fr = 0.8, the flow is classified as:

A Supercritical

B Subcritical

C Critical

D Transitional

Correct Answer: B. Subcritical

EXPLANATION

Fr < 1 indicates subcritical (tranquil) flow, Fr = 1 is critical, and Fr > 1 is supercritical (rapid) flow. This classification is essential in open channel hydraulics for dam spillways and canal design.

Test

Q.4 Medium Fluid Mechanics

A submerged gate in a canal discharges water at the bottom. The discharge through the gate is given by Q = Cd × A × √(2g(h₁-h₂)), where Cd is discharge coefficient, A is gate area, and (h₁-h₂) is head difference. Typical value of Cd for a sharp-edged gate is:

A 0.55-0.65

B 0.75-0.85

C 0.95-1.00

D 1.05-1.10

Correct Answer: A. 0.55-0.65

EXPLANATION

For sharp-edged submerged gates, Cd ≈ 0.6. For rounded gates Cd ≈ 0.8. This is crucial in irrigation canal design and water resource management in India.

Test

Q.5 Hard Fluid Mechanics

According to the theory of boundary layer flow, the boundary layer thickness δ grows along a flat plate as δ ∝ √(νx/V). This relationship is derived from:

A Euler's equation

B Prandtl's momentum integral equation

C Navier-Stokes equations with boundary layer approximations

D Continuity equation alone

Correct Answer: C. Navier-Stokes equations with boundary layer approximations

EXPLANATION

The √x dependence comes from solving the Navier-Stokes equations with boundary layer approximations (Blasius solution). This is fundamental to aerodynamic design in Indian aircraft industries.

Test

Q.6 Hard Fluid Mechanics

The specific speed of a turbine is Ns = N√Q/H^1.25, where N is speed in rpm, Q is discharge in m³/s, and H is head in meters. A turbine with Ns < 50 is classified as:

A Pelton turbine (impulse)

B Turgo turbine

C Francis turbine (reaction)

D Kaplan turbine (axial flow)

Correct Answer: A. Pelton turbine (impulse)

EXPLANATION

Specific speed Ns < 50 indicates Pelton turbines, 50-250 indicates Francis turbines, and >250 indicates Kaplan turbines. This classification is essential in hydroelectric projects across Indian dams.

Test

Q.7 Hard Fluid Mechanics

For pipe flow, the friction factor f in the Moody diagram depends on both Reynolds number and relative roughness (ε/D). For a rough pipe with high Re, f approaches an asymptotic value independent of Re. This region is called:

A Laminar region

B Fully turbulent region (complete turbulence)

C Transition region

D Creeping flow region

Correct Answer: B. Fully turbulent region (complete turbulence)

EXPLANATION

At very high Reynolds numbers in rough pipes, friction factor depends only on relative roughness, not Re. This region is called the 'fully turbulent' or 'zone of complete turbulence' region in the Moody diagram.

Test

Q.8 Hard Fluid Mechanics

The Mach number M = V/a represents the ratio of flow velocity to the speed of sound. For subsonic compressible flow in a converging nozzle, what occurs to the Mach number as the flow accelerates?

A Mach number decreases

B Mach number remains constant

C Mach number increases

D Mach number becomes negative

Correct Answer: C. Mach number increases

EXPLANATION

In a converging nozzle with subsonic inlet flow, velocity increases and Mach number increases as flow approaches throat. This principle is critical in rocket propulsion and aerospace applications in India.

Test

Q.9 Hard Fluid Mechanics

For a Venturi tube with throat area ratio A₁/A₂ = 3 and upstream pressure P₁ = 200 kPa, assuming inviscid flow (Bernoulli applicable), if the pressure at throat P₂ drops to 80 kPa, the upstream velocity V₁ is (ρ = 1000 kg/m³):

A 6.5 m/s

B 8.2 m/s

C 10.5 m/s

D 12.8 m/s

Correct Answer: C. 10.5 m/s

EXPLANATION

From Bernoulli: P₁/ρg + V₁²/2g = P₂/ρg + V₂²/2g. Using continuity A₁V₁ = A₂V₂, and solving: V₁ = √(2(P₁-P₂)/(ρ(A₂²/A₁²-1))) ≈ 10.5 m/s. Venturi tubes are standard in flow measurement systems.

Test

Q.10 Hard Fluid Mechanics

The momentum equation for a control volume states that ΣF = d(mV)/dt. For a fluid jet deflected by a flat plate at angle θ to the horizontal, the force perpendicular to the original jet direction depends on:

A Only the jet velocity

B Only the deflection angle

C Both jet velocity and deflection angle (sinθ component)

D The density of the fluid only

Correct Answer: C. Both jet velocity and deflection angle (sinθ component)

EXPLANATION

The perpendicular force component = ρQV²sin(θ), where Q is discharge and V is velocity. This principle is used in water turbines and industrial jet applications.

Test

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