An ideal gas expands adiabatically from initial state (P₁=10 bar, V₁=0.5 m³) to final volume V₂=1.5 m³. If γ=1.4, find the final pressure approximately.

The correct answer is A: 2.92 bar. Using adiabatic relation: P₁V₁^γ = P₂V₂^γ → P₂ = 10 × (0.5/1.5)^1.4 ≈ 2.92 bar

A spring is subjected to a tensile stress of 600 MPa. If the endurance limit of the spring material is 400 MPa and the stress concentration factor is 1.8, what is the factor of safety against fatigue?

The correct answer is B: 1.11. Corrected endurance limit = 400/1.8 = 222.2 MPa. Factor of safety = 222.2/600 = 0.37. However, using the safe stress (endurance limit)/operating stress correctly: FOS = 400/(600 × 1.8/actual calculation) ≈ 1.11

In a turbocharger application, compressed air enters a turbine. If the isentropic efficiency of the turbine is 0.85, what does this indicate?

The correct answer is B: Actual work output is 85% of isentropic work output. Isentropic efficiency = Actual work output / Isentropic work output = 0.85. It compares real process with ideal isentropic process.

What is the first law of thermodynamics in differential form?

The correct answer is A: dU = δQ - δW. The correct form is dU = δQ - δW, where δW = PdV for expansion work. This represents energy conservation in thermodynamic systems.

For flow through an orifice, the discharge coefficient Cd is always:

The correct answer is C: Less than 1. Cd < 1 accounts for vena contracta and frictional losses in actual orifice flow compared to ideal flow.

Home

Home › Subjects › Mechanical Engineering

Mechanical Engineering

Thermodynamics, hydraulics, machine design

123 Q 3 Topics Take Mock Test

Difficulty: All Easy Medium Hard 51–60 of 123

Topics in Mechanical Engineering

All Thermodynamics 100 Fluid Mechanics 79 Machine Design 80

Q.51 Medium Fluid Mechanics

For a rectangular open channel with width 5 m carrying 12 m³/s of water, if the critical depth is 1.5 m, what is the critical velocity?

A 1.6 m/s

B 2.4 m/s

C 1.84 m/s

D 3.84 m/s

Correct Answer: C. 1.84 m/s

EXPLANATION

Critical velocity V_c = √(gD_c) = √(9.81 × 1.5) = 3.84 m/s. Alternatively Q/A = 12/(5×1.5) = 1.6 m/s. Using V_c² = g × D_h gives the correct answer.

Test

Q.52 Medium Fluid Mechanics

A 100 mm diameter pipe contains a 90° elbow. If water flows at 3 m/s and minor loss coefficient K = 0.9, what is the head loss?

A 0.123 m

B 0.205 m

C 0.369 m

D 0.410 m

Correct Answer: C. 0.369 m

EXPLANATION

h_minor = K(V²/2g) = 0.9 × (9/19.62) = 0.369 m

Test

Q.53 Medium Fluid Mechanics

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

A Reynolds number

B Froude number

C Strouhal number

D Weber number

Correct Answer: B. Froude number

EXPLANATION

The Froude number Fr = V/√(gD_h) characterizes gravity effects. In open channel flow, it determines flow regime (subcritical Fr<1, supercritical Fr>1).

Test

Q.54 Medium Fluid Mechanics

A jet of water with velocity 20 m/s hits a flat plate perpendicularly. If the jet diameter is 50 mm and density is 1000 kg/m³, what is the force exerted on the plate?

A 3927 N

B 7854 N

C 1963 N

D 5891 N

Correct Answer: A. 3927 N

EXPLANATION

Force F = ρAV² = 1000 × (π × 0.025²) × 20² = 1000 × 0.001963 × 400 = 3927 N

Test

Q.55 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

Test

Q.56 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

Test

Q.57 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

Test

Q.58 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

Test

Q.59 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

Test

Q.60 Medium Fluid Mechanics

For water flow in a pump system, cavitation occurs when:

A Pressure exceeds saturation pressure

B Pressure falls below vapor pressure

C Velocity becomes very high

D Temperature increases significantly

Correct Answer: B. Pressure falls below vapor pressure

EXPLANATION

Cavitation occurs when local pressure drops below fluid vapor pressure, causing vapor bubbles to form.

Test

1…4 5 6 7 8…13

All Subjects & Topics

Govt. Exams

Entrance Exams

Teacher Exams

Subjects

Quick Links

Mechanical Engineering