The Graduate Aptitude Test in Engineering (GATE) is one of the most popular exams for engineering graduates in India. It tests conceptual knowledge and problem-solving abilities across various engineering disciplines.

## 25 important GATE questions in Mechanical Engineering that test key concepts:

- In a four-stroke diesel engine, the thermal efficiency mainly depends on:

a) Compression ratio

b) Cetane number of fuel

c) Ignition quality of fuel

d) Viscosity of lubricating oil

Answer: a

Explanation: Thermal efficiency of a diesel engine primarily depends on the compression ratio. Higher the compression ratio, higher is the thermal efficiency.

- The power transmitted by a shaft is maximum when the angle between the torque and angular velocity vectors is:

a) 0°

b) 45°

c) 90°

d) 180°

Answer: c

Explanation: Power transmitted by a shaft is given by P=Tω. It is maximum when T and ω are perpendicular to each other.

- …, …, …, … are the four links of a four bar chain mechanism. The instantaneous center for the linkage between links 2 and 3 lies on link:

a) 1

b) 2

c) 3

d) 4

Answer: d

Explanation: The instantaneous center (IC) between two links lies on the line perpendicular to both links. For links 2 and 3, the IC lies on link 4.

- The temperature gradient in a thin rectangular fin of uniform cross-section is proportional to:

a) Distance from the fixed end

b) Square of the distance from the fixed end

c) Cube of the distance from the fixed end

d) Fourth power of the distance from the fixed end

Answer: b

Explanation: In a straight fin with uniform cross-section, the temperature gradient is proportional to the square of the distance from the fixed end.

- Elliptical gears are used to avoid:

a) Backlash

b) Interference

c) Undercutting

d) Noise

Answer: b

Explanation: Elliptical gears are shaped so the contact points shift along the line of action, avoiding interference.

- The velocity ratio of a simple screw jack with the square threaded screw is:

a) Equal to helix angle

b) Equal to reciprocal of helix angle

c) Equal to pi divided by helix angle

d) Equal to reciprocal of pi divided by helix angle

Answer: d

Explanation: Velocity ratio of a screw jack = 1/(π. tan α), where α is the helix angle.

- In a closed cycle gas turbine, the process 2-3 involves:

a) Isentropic compression

b) Constant pressure heat rejection

c) Isentropic expansion

d) Constant pressure heat addition

Answer: d

Explanation: 2-3 is the constant pressure heat addition process in the Brayton cycle.

- cavitation in pumps can be avoided by:

a) Increasing suction head

b) Decreasing suction lift

c) Increasing impeller diameter

d) Reducing speed

Answer: b

Explanation: Cavitation occurs due to low pressure at pump inlet. It can be avoided by reducing suction lift.

- The power transmitted by a belt is maximum when:

a) Belt is just about to slip

b) Tension on tight side is twice the tension on slack side

c) Tension on tight side is thrice the tension on slack side

d) Tension on slack side is zero

Answer: c

Explanation: For maximum power transmission, T1/T2 = e^μα , where μ is coefficient of friction and α is contact angle.

- In a turning operation, the cutting speed is increased to increase:

a) Material removal rate

b) Chip-tool contact length

c) Effective rake angle

d) Surface finish

Answer: a

Explanation: Higher cutting speed increases the material removal rate in turning.

- ——- theory is used to determine the critical speed of a shaft.

a) Castigliano’s

b) Rankine’s

c) Euler’s

d) Coulomb’s

Answer: b

Explanation: Critical speed of a shaft is determined by Rankine’s theory.

- —— separates the boundary layer from the surface of an aerofoil.

a) Venturi

b) Pitot tube

c) Orifice meter

d) Boundary layer trips

Answer: d

Explanation: Boundary layer trips are devices put on aerofoil surfaces to deliberately separate the boundary layer.

- In a closed cycle gas turbine, the purpose of regeneration is:

a) To decrease thermal efficiency

b) To increase specific work output

c) To increase thermal efficiency

d) To decrease work ratio

Answer: c

Explanation: Regeneration increases thermal efficiency of a gas turbine cycle by preheating the air before combustion.

- ——- theory is used to design leaf springs.

a) Castigliano’s

b) Euler’s

c) Rankine’s

d) Hooke’s law

Answer: a

Explanation: Deflection of leaf springs is determined by Castigliano’s theorem.

- ——— bearings are used to support heavy radial loads at low speeds.

a) Ball

b) Roller

c) Journal

d) Thrust

Answer: b

Explanation: Roller bearings support heavy radial loads at low speeds better than ball bearings.

- In a turning operation on a steel bar, the chip thickness ratio is 0.3. The shear plane angle is:

a) 16.7°

b) 26.6°

c) 30°

d) 63.4°

Answer: b

Explanation: Chip thickness ratio = Sin φ, where φ is shear plane angle.

- Volumetric efficiency of a reciprocating compressor decreases with:

a) Increase in clearance volume

b) Decrease in clearance volume

c) Increase in speed

d) Increase in pressure ratio

Answer: a

Explanation: Clearance volume reduces volumetric efficiency of a compressor.

- Dynamic load capacity of a ball bearing is proportional to:

a) Ball diameter to the power 3

b) Ball diameter to the power 2

c) Ball diameter to the power 1.5

d) Ball diameter to the power 1

Answer: c

Explanation: Dynamic capacity ∝ d^1.5, where d is ball diameter.

- Tool life in a turning operation on cast iron is 600 min when cutting speed is 100 m/min. If the cutting speed is doubled, the tool life will become:

a) 150 min

b) 225 min

c) 300 min

d) 600 min

Answer: a

Explanation: Tool life is inversely proportional to cutting speed.

- —– is the heat treatment process used to increase surface hardness of steel parts.

a) Annealing

b) Normalizing

c) Hardening

d) Tempering

Answer: c

Explanation: Hardening increases hardness by rapid cooling after austenitizing.

- —— theory determines deflection in beams subjected to transverse loading.

a) Castigliano’s

b) Euler’s

c) Rankine’s

d) Bernoulli’s

Answer: d

Explanation: Deflection of beams is given by Bernoulli-Euler beam theory.

- Volumetric efficiency of a reciprocating air compressor depends upon:

a) Clearance factor

b) Speed

c) Pressure ratio

d) All of the above

Answer: d

Explanation: Volumetric efficiency depends on clearance factor, speed and pressure ratio.

- In orthogonal machining, —– is used to measure surface finish.

a) Taylor’s tool life equation

b) Merchant’s circle diagram

c) Chip reduction coefficient

d) Centre-line average roughness

Answer: d

Explanation: Surface finish is quantified by the centre-line average roughness (Ra) value.

- —— separates the turbulent boundary layer from the surface of an aerofoil.

a) Prandtl tube

b) Pitot tube

c) Venturi

d) Unsteady shock wave

Answer: d

Explanation: Unsteady shock waves cause boundary layer separation on aerofoils.

- —— is the heat treatment process used to relieve internal stresses in steel parts.

a) Hardening

b) Annealing

c) Normalizing

d) Tempering

Answer: b

Explanation: Annealing relieves internal stresses by slow cooling after heating.

This covers some of the key topics in Mechanical Engineering that are important from the GATE exam perspective. These questions test conceptual knowledge on thermodynamics, strength of materials, machine design, manufacturing processes, fluid mechanics, and heat transfer. Practicing such questions will help GATE aspirants assess their level of preparation and improve their problem-solving speed and accuracy.