Mechanical Interview Questions and Answers

1. What is gear ratio?

A - gear ratio (gr) = (number of teeth on output or driven gear)/(number of teeth on input or driver gear)

Gear ratio can also be expressed as the relationship between the pitch circles of both wheels (where d is the pitch diameter of the input wheel and D is the pitch diameter of the output wheel):

2. What is pressure exerted by 1m of water column?

A – 0.1 Kg/cm2

3. What is anomalous expansion of water?

A - The maximum density of water occurs at 4 °C. It has the anomalous property of becoming less dense, not more, when it is cooled down to its solid form, ice. It expands to occupy 9% greater volume in this solid state, which accounts for the fact of ice floating on liquid water.4. What is unit of specific density of air.

4. What is unit of specific density of air?

A - Dimensionless

5. What is viscosity?

A - Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress.

6. What is Reynolds number?

A - In fluid mechanics, the Reynolds number Re is a dimensionless number that gives a measure of the ratio of inertial forces to viscous forces and consequently quantifies the relative importance of these two types of forces for given flow conditions.

7. What is Mach number?

Mach number (Ma or M) is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure. It is commonly used to represent the speed of an object when it is traveling close to or above the speed of sound.

8. What is the speed of sound?

- 340 m/s

9. During rainy season even though thunder occurs first followed by lightning; why do we see lightning first and then hear the thunder?

- Light travels faster than sound

10. What happens when you put petrol into the diesel engine?

- Petrol in a Diesel engine is actually worse. Petrol is a lot more likely to ignite under the conditions in a Diesel engine, but it'll ignite too soon and burn too fast compared to what the engine will expect. The crankshaft will not complete a full revolution and it shall knock. It might run, but very rough. The engine will be damaged very badly and life will be reduced. 

11. What is knocking?

- Knocking (also called knock, detonation, spark knock, pinging or pinking) in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.

12. What is the Zeroth law of thermodynamics?

- The zeroth law states that if two systems are in thermal equilibrium with a third system, they are also in thermal equilibrium with each other.

13. What is the 1^st, 2^nd and 3^rd law of thermodynamics?

• The first law of thermodynamics expresses the existence of a quantity called the internal energy of a system, and shows how it is related to the distinction between energy transfer as work and energy transfer as heat. The internal energy obeys the principle of conservation of energy but work and heat are not defined as separately conserved quantities. Equivalently, the first law of thermodynamics states that perpetual motion machines of the first kind are impossible.

• The second law of thermodynamics expresses the existence of a quantity called the entropy of a system and states that the entropy of an isolated macroscopic system never decreases, or, equivalently, that perpetual motion machines of the second kind are impossible.

• The third law of thermodynamics concerns the entropy of a perfect crystal at absolute zero temperature, and implies that it is impossible to cool a system to exactly absolute zero, or, equivalently, that perpetual motion machines of the third kind are impossible.

14. What is rankine cycle?

- The Rankine cycle is a cycle that converts heat into work. The heat is supplied externally to a closed loop, which usually uses water. This cycle generates about 80% of all electric power used throughout the world, including virtually all solar thermal, biomass, coal and nuclear power plants.

16. State the applications of compressor in day to day life?

- Air conditioners, Refrigerators

17. What is the function of foot valve in the well?

- It acts like a NRV. Prevents water flow back into the well and facilitates priming. 

18. What are the types of turbines?

- Impulse and Reaction

19. Why chimney is normally tapered?

- For draft

20. Which one cools faster – A square plate held horizontal or A square plate held vertical?

- Vertical. Because the radiation due to the bottom face of the horizontal face in turn heats the top surface of the plate.