70 Important Mechanical Engineering Interview Questions and Answers

For the placement in the top mechanical engineering companies, it is very necessary to learn and practice for the most important mechanical engineering interview questions and answers.

During the interview, the HR team can ask you the mechanical engineering technical questions to examine your knowledge about your subject and field. If you planning to appear in the job interview, these frequently asked mechanical engineering questions and answers will help you.

These mechanical engineering interview questions and answers are meant for the purpose of a job interview and getting an idea of interview question.

We will soon publish diploma mechanical engineering interview questions and basic interview questions for mechanical design engineer. However, these questions are also important if you are looking for basic interview questions for mechanical engineer freshers or job interview questions for mechanical engineer.

Two Common Job Interview Questions for Mechanical Engineer

Before going into Mechanical Engineering Interview Questions and Answers let us discuss the very first two job interview questions for mechanical engineers. These are common to almost every mechanical engineering job interview.

Q. What is Mechanical Engineering?

Answer – Mechanical engineering is the discipline that applies the principles of engineering, physics, and materials science for the design, analysis, manufacturing, and maintenance of mechanical systems.

It is the branch of engineering that involves the design, production, and operation of machinery. It is one of the oldest and broadest of the engineering disciplines.

The mechanical engineering field requires an understanding of core areas including mechanics, kinematics, thermodynamics, materials science, structural analysis, and electricity.

Mechanical engineers use these core principles along with tools like computer-aided design, and product lifecycle management to design and analyze manufacturing plants, industrial equipment and machinery, heating and cooling systems, transport systems, aircraft, watercraft, robotics, medical devices, weapons, and others.

Q. What are Sub-disciplines of Mechanical Engineering?

Answer – The sub-disciplines of Mechanical engineering are Mechanics, Mechatronics and robotics, Structural analysis, Thermodynamics and thermo-science & Design and drafting.


Mechanical Engineering Interview Questions and Answers

Q1. What is annealing?

Answer – It is a process of heating a material above the re-crystallization temperature and cooling after a specific time interval. This increases the hardness and strength if the material.

Q2. What is ductile-brittle transition temperature?

Answer – It is the temperature below which the tendency of a material to fracture increases rather than form. Below this temperature, the material loses its ductility. It is also called Nil Ductility Temperature.

Q3. Which theories of failure are used for (a) ductile materials and (B) brittle materials?

Answer – For ductile materials, theories of failure used are maximum shear stress theory, and maximum energy of distortion theory; while for brittle materials, the theory of maximum principal stress, and maximum strain are used.

Q4. What does thermal diffusivity of metals signify?

Answer – Thermal diffusivity is associated with the speed of propagation of heat into solids during changes in temperature with time.

Q5. What is enthalpy?

Answer – Enthalpy is the heat content of a chemical system.

Q6. What is a positive displacement pump?

Answer – A positive displacement pump causes a liquid or gas to move by trapping a fixed amount of fluid or gas and then forcing (displacing) that trapped volume into the discharge pipe. Positive displacement pumps can be further classified as either rotary-type (for example the rotary vane) or lobe pumps similar to oil pumps used in car engines. These pumps give a non-pulsating output or displacement, unlike the reciprocating pumps. Hence, they are called positive displacement pumps. Which parameter remains constant in a throttling process?

Q7. Which parameter remains constant in a throttling process?

Answer – Enthalpy

Q8. Which reactor produces more fissionable material than it consumes?

Answer – Breeder reactor.

Q9. Which reactor uses natural uranium as fuel?

Answer – Gas-cooled reactor.

Q10. Which reactor uses heavy water as a moderator?

Answer – CANDU.

Q11. Which reactor requires no moderator? 

Answer – Breeder reactor.

Q12. What is ferrite?

Answer – Magnetic iron rock

Q13. What is the difference between projectile motion and a rocket motion?

Answer – A projectile has no motor/rocket on it, so all of its momenta is given to it as it is launched. An example of a projectile would be a pen that you throw across a room.

A rocket or missile does have a motor/rocket on it so it can accelerate itself while moving and so resist other forces such as gravity.

Q14. Explain Otto cycle.

Answer – Otto cycle can be explained by a pressure-volume relationship diagram. It shows the functioning cycle of a four-stroke engine. The cycle starts with an intake stroke, closing the intake and moving to the compression stroke, starting of combustion, power stroke, heat exchange stroke where heat is rejected and the exhaust stroke. It was designed by Nicolas Otto, a German engineer.

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Q15. What is a converter reactor? 

Answer – A reactor plant which is designed to produce more fuel than it consumes. The breeding is obtained by converting fertile material to fissile material.

Q16. Explain nuclear reactor in brief.

Answer – A plant which initiates, sustains, controls and maintains nuclear fission chain reaction and provides shielding against radioactive radiation is the nuclear reactor.

Q17. What is gear ratio?

Answer – It is the ratio of the number of revolutions of the pinion gear to one revolution of the idler gear.

Q18. Which heating value is indicated by a calorimeter and why?

Answer – Gross heating value because steam is condensed and heat of vapour formed is recovered.

Q19. What is annealing?

Answer – It is a process of heating a material above the re-crystallization temperature and cooling after a specific time interval. This increases the hardness and strength if the material.

Q20. What is fuel ratio? 

Answer – Fuel ratio is the ratio of its % age of fixed carbon to volatile matter.12. What is ductile-brittle transition temperature?

Q21. What is ductile-brittle transition temperature?

Answer – It is the temperature below which the tendency of a material to fracture increases rather than form. Below this temperature, the material loses its ductility. It is also called Nil Ductility Temperature.

Q22. On which analysis is based the Dulong’s formula for the heating value of fuel?

Answer – On ultimate analysis.

Q23. Which element causes a difference in higher and lower heating values of fuel?

Answer – Hydrogen.

Q24. What is a uniformly distributed load?

Answer – A UDL or uniformly distributed load is a load, which is spread over a beam in such a way that each unit length is loaded to the same extent.

Q25. How is martensite structure formed in steel?

Answer – Martensite transformation begins when austenite is cooled below a certain critical temperature, called the martensite start temperature. As we go below the martensite start temperature, more and more martensite forms and complete transformation occurs only at a temperature called martensite finish temperature. Formation of martensite requires that the austenite phase must be cooled rapidly.

Q26. Which two elements have the same percentage in the proximate and ultimate analysis of coal?

Answer – Moisture and ash.

Q27. What is an orthographic drawing?

Answer – Orthographic projections are views of a 3D object, showing 3 faces of it. The 3 drawings are aligned so that if the page were folded, it would create part of the shape. It is also called multiview projections.

The 3 faces of an object consisting of its plan view, front view and side view. There are 2 types of orthographic projection, which are 1st angle projection and 3rd angle projection.

Q28. Which reactor has no moderator? Ans: Fast breeder reactor

Answer – Fast breeder reactor

Q29. What is representative elementary volume?

Answer – Smallest volume over which measurements can be made that will yield a representative of the whole.

Q30. Ultimate analysis of coal is elementary analysis. What is it concerned with? 

Answer – Carbon, hydrogen, nitrogen, and sulphur in coal on a weight percentage basis.

Q31. Why are LNG pipes curved?

Answer – LNG pipes are curved because LNG is condensed gas (-164 deg cel) so it can expand the pipes that are what engineers designed the LNG pipes are the curved type.

Q32. Quantities like pressure, temperature, density, viscosity, etc. are independent of mass. What are these called?

Answer – Intensive properties.

Q33. What does angular momentum mean?

Answer – Angular momentum is an expression of an object’s mass and rotational speed. Momentum is the velocity of an object times it is mass, or how fast something is moving how much it weigh.

Therefore, angular momentum is the object’s mass times the angular velocity where the angular velocity is how fast something is rotating expressed in terms like revolutions per minute or radians per second or degrees per second.

Q34. What is the effect of inter cooling in gas turbines? 

Answer – It decreases thermal efficiency but increases net output

Q35. Can you use motor oil in a hydraulic system?

Answer – Hydraulic fluid has to pass a different set of standards than motor oil. Motor oil has tackifiers, lower sulphur content, and other ingredients that could prove harmful to the seals and other components in a hydraulic system. If it is an emergency only should do it.

Q37. What is the effect of friction on the flow of steam through a nozzle?

Answer – To decrease both mass flow rate and wetness of steam

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Q38. What causes white smoke in two-stroke locomotive engines?

Answer – That is the engine running too lean (lack of fuel). This condition will lead to overheating and failure of the engine.

Q39. Out of electric heater and heat pump, which is economical in operation?

Answer – Heat pump.

Q40. What is the role of nitrogen in welding?

Answer – Nitrogen is used to prevent porosity in the welding member by preventing oxygen and air from entering the molten metal during the welding process. Other gasses are also used for this purpose such as Argon, Helium, Carbon Dioxide, and the gasses are given off when the flux burns away during SMAW (stick) welding.

Q41. Which furnace burns low-ash fusion coal and retains most of the coal ash in the slag? Ans: Cyclone furnace.

Answer – Cyclone furnace.

Q42. What does Greenfield project mean?

Answer – Greenfield projects are those projects, which do not create any environmental nuisance (pollution), follows environmental management system and EIA (environment impact assessment). These projects are usually of big magnitude.

Q43. Why is boiler purged every time before starting firing of fuel? 

Answer – Purging ensures that any unburnt fuel in the furnace is removed, otherwise it may lead to explosion34. Is it the stress that, produces strain or strain produces stress?

Q44. Is it the stress that, produces strain or strain produces stress?

Answer – A Force applied to an object will cause a displacement. The strain is effectively a measure of this displacement (change in length divided by original length).

Stress is the Force applied divided by the area it is applied. (E.g. pounds per square inch)
Therefore, to answer the question, the applied force produces both Stress and Strain. Stress and Strain are linked together by various material properties such as Poisson’s ratio and Young’s Modulus.

Q45. What is the principle of mechanical refrigeration?

Answer – A volatile liquid will boil under the proper conditions and in so doing will absorb heat from surrounding objects.

Q46. How does iron ore turn into steel?

Answer – To make Steel, Iron Ore is refined into iron and all the carbon is burned away using very high heat (Bessemer). A percentage of Carbon (and other trace elements) are added back to make steel. 36. What is knurling?

Knurling is a machining process normally carried on a centre lathe. The act of Knurling creates a raised crisscross pattern on a smooth round bar that could be used as a handle or something that requires extra grip.

Q47. What type of boiler does not need a steam drum?

Answer – Supercritical pressure boiler.

Q48. What is the mechanical advantage of a double pulley?

Answer – It only takes half the effort to move an object but twice the distance.

Q49. Why are large boilers water tube type? 

Answer – Water tube boilers raise steam fast because of large heat transfer area and positive water circulation. Thus they respond faster to fluctuations in demand. Further single tube failure does not lead to catastrophe.

Q50. What is extruded aluminium?

Answer – Extrusion is the process where a metal or a metal bar is pulled through a mandrel to elongate it and/or give it a final shape.

Extruded Aluminum is a common form of making small aluminium wire, bars or beams and many varieties of small non-structural, decorative pieces.

Q51. What is the difference between hard water and soft water? 

Answer – Hard water contains an excess of scale forming impurities and soft water contains very little or no scale forming substances.

Q52. What is a Newtonian fluid?

Answer – A Newtonian fluid possesses a linear stress-strain relationship curve and it passes through the origin. The fluid properties of a Newtonian fluid do not change when any force acts upon it.

Q53. What is caustic embrittlement? 

Answer – It is the actual physical change in metal that makes it extremely brittle and filled with minute cracks. It occurs particularly in the seams of riveted joints and around the rivet holes.

Q54. What are the points in the stress-strain curve for steel?

Answer – Proportional limit, elastic limit or yield point, ultimate stress and stress at failure.

Q55. When is maximum discharge obtained in nozzle?

Answer – At the critical pressure ratio

Q56. How much is the work done in an isochoric process? 

Answer – Zero

Q57. What does F.O.F. stand for in the piping design?

Answer – FOF stands for Face of Flange. A flange has either of the two types of faces:

a) Raised face
b) Flat face

The F.O.F is used to know the accurate dimension of the flange in order to avoid the minute errors in measurement in case of vertical or horizontal pipelines.

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Q58. Explain Otto cycle.

Answer – Otto cycle can be explained by a pressure-volume relationship diagram. It shows the functioning cycle of a four-stroke engine. The cycle starts with an intake stroke, closing the intake and moving to the compression stroke, starting of combustion, power stroke, heat exchange stroke where heat is rejected and the exhaust stroke. It was designed by Nicolas Otto, a German engineer.

Q59. What is the mechanism?

Answer – A mechanism is an assembly of different parts which perform a complete motion and is often part of a machine.

Q60. State the laws of thermodynamics

Answer – Thermodynamics is a physical science which studies the interrelation between heat, work and the internal energy of any system. Thermodynamics helps study all the systems of mechanical engineering. There are three laws of thermodynamics.

First Law: Energy can be neither created nor destroyed. It can only change forms. In any process in an isolated system, the total energy remains the same.

Second Law: The second law of thermodynamics states that the entropy of any isolated system not in thermal equilibrium almost always increases.

Third Law: As the temperature approaches absolute zero, the entropy of a system approaches a minimum.

Q61. What is Hess law?

Answer – According to the Hess law, the energy transfer is simply independent of the way being followed. If the reactant and the product of the whole process are the same then the same amount of energy will be dissipated or absorbed.

Q62. What is PS?

Answer – Personal Statement. It is something that gives an informative background about an individual.

Q63. What is a bearing? What are the different types of bearings?

Answer – The bearing is a device that helps smoother movement with minimal friction which in turn helps enhances efficiency and speed. Considering two types of loading, radial, and thrust, there are different types of bearings which help handle these loads. The basic difference in the types of loads is essentially due to their ability to handle the weight and different kinds of loads for various applications. Different types of bearings are:

(a) Ball bearing
(b) Roller bearing
(c) Ball Thrust bearing
(d) Roller thrust bearing
(e) Tapered roller bearing
(f) Magnetic bearings
(g) Giant Roller Bearing

Q64. What is a time and motion theory?

Answer – Frederick Taylor was a pioneer of the time and motion theory. This technique monitors the amount of time required to complete a task along with observing the steps taken by a worker to complete the given task.

Q65. Which is the hardest material on earth?

Answer – Diamond is currently the hardest material, made up of carbon atoms which cannot move. Carbon is the only atom that can have four electrons in the second shell surrounding the carbon nucleus, precisely why making a diamond the hardest material. However, there also are claims by a few to a new rare material called Wurtzite Boron Nitride which has a structure similar to a diamond but has some other atoms in place of carbon.

Q66. One unit of BTU is how many Joules?

Answer – 1 BTU=1055.06 Joules

Q67. What does a pump develop? Give the reason to support your answer.

Answer – The pump is a device that is used to transfer fluid from one place to another place which means it develops flow not pressure.

Q68. Explain the difference between pipe and a tube.

Answer – A pipe is measured based on its inner diameter (ID) whereas a tube is measured based on the outer diameter (OD). Other than the dimensions there is no major difference between the two.

Q69. What is Bauschinger effect?

Answer – According to Bauschinger, the limit of proportionality of material does not remain constant but varies according to the direction of stress under cyclic stresses

Q70. List two effects of manganese in plain carbon steels.

Answer – Manganese increases tensile strength and hardness. It decreases weldability.

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