Mechanical engineering Questions and Answers

1. Least count of a Vernier metric micrometer ?
ans. 0.001mm

(A vernier micrometer is used for measurement purposes. The metric micrometer looks similar like an ordinary micrometer. The difference between both are graduations on the sleeve and the barrel. There are two seperate lines on the sleeve of metric micrometer. The lower row contains millimeter graduations and the upper row represents one half millimeter. Thimble moves the spindle 0.5 mm on each complete turn. The vernier metric micrometer has an ability to measure about two thousands of a mm.)

2. A chemical compound of carbon with iron is called ?
ans. Cementite
(Cementite is an intermetallic component of Iron and Carbon. Commonly called as Iron Carbide with formula Fe3C. It has an orthorhombic crystal structure with 6.67%Carbon and 93.3% Iron. Simply for your knowledge lets assume You have iron and Coke available as raw materials. Coke is obtained from Coking of Coal by carbonisation. Now heat them together in a furnace upto melting temperature. Approximately 1540 degree. For solidification we have to reduce its temperature from 1540-1200. We get a BCC structure called as delta ferrite. Again on cooling structure changes to FCC and we get Austenite 723 at degree( This temperature also called as austenitising temperature). On cooling down further austenite changes to pearlite (alpha ferrite+Cementite). 
Ferrite: Pure steel with less carbon
Cementite: Relatively harder which contains 6.67% Carbon
Pearlite: Which contains both ferrite and Cementite formed after Eutectoid reaction at 723 degrees.
Austenite: FCC Structure exists above 723 degree )

3. A welding rectifier is used to:
ans. Convert an AC welding supply into DC supply
(A welding rectifier converts AC to DC supply and maintains the stability of arc in arc welding.)

4. Testing a weld without damaging the joint is called ?
ans. Non destructive testing
(NDT evaluates the properties of material without causing any damage to the material. Six most frequently used NDT methods are Eddy current, Magnetic particle, Liquid penetrant, Radiographic, Ultrasonic and Visual testing. These tests reveal weak or defective sections that can be corrected before the material released to be used outside)

5. A sine bar is used for :
ans. Finding the angle of a taper job
(Its an instrument used to measure angles. It has two cylindrical plugs or rollers lapped and a accurate straight rectangular bar. A sine bar is specified by the centres of two rollers. Its principle is based on trigonometry 

Sin value of a right angled triangle Opposite/ Hypotnuse

6. Mass per unit volume of a fluid?
ans. Density
(Density of a substance is the relationship between mass of certain quantity of fluid and how much space it takes to occupy. Size, Mass and arrangement of molecules inside a particle determines the density of that substance.)

7. Force per unit area at a point ?
ans. Pressure
(Force applied perpendicular to the surface of an object per unit area which is that force exerted. SI unit for pressure is Pascal. A system under pressure has potential to perform work on its sorroundings, So pressure is the measure of potential energy stored per unit volume.)

8. Momentum of a body?
ans. Mass x Velocity


9. Watt is the unit of:
ans. Power

10. One metric Horse power ?
ans. 736 watts

11. Copper Tin alloy?
ans.  Bronze

12. EDM stands for:
ans. Electro discharge Machining

13. For cutting operation,  the most suitable flame is ?
ans. Neutral

14. Within the elastic limit in a loaded material,  stress is:
ans. Directly proportional to strain

15. Files are made of:
ans. High carbon steel

16. Accuracy of metric micrometer ?
ans. 0.01mm

17. Gauge used to measure gap between mating parts?
ans. Feeler gauge

18. Scribers are made of :
ans. High carbon steel

19. The process of bevelling the end of hole is called:
ans. Counter sinking

20. The accuracy of vernier bevel protractor is:
ans. Five minute

21. In a static fluid
ans. only normal stresses can exist

22. A fluid is said to be ideaal if it is
ans. inviscous and incompressible

23. An ideal fluid must fullfill
ans. continuity equation

24. If no resistance is encountered by displacement such substance is called
ans. ideal fluid

25. The volumetric change of the fluid caused by a resistance is known as 
ans. compressibility

26. density of water is maximum at 
ans. 4degree

27. The value of mass density in kgsecm^4 for water at o degree is 
ans. 101.9
28. Property of a fluid by which its own molecules are attracted together is called
ans. cohesion

29. Mercury does not wet the glass, this is due to property called
ans. surface tension

30. The property of a fluid to resist tensile stress is called
ans. cohesion

31. Property of a fluid by which different molecules are attracted together is called
ans. adhesion

32. The specific weight of water is 1000kg/m3
ans. at normal pressure 760mm, at mean sea level, at 4degree temperature

33. Specific weight of water in SI unts
ans. 9.81*10^3 N/m3

34. When flow parameters at any instant remains the same at every point then flow said to be
ans. uniform

35. A dimensionless quantity
ans. specific gravity

36. The normal stress in a fluid will be constant in all directions at a point only if
ans. it is at rest

37. The pressure at a point in a fluid will not be same at all direction if
ans. it is viscous and moving

38. An object having 10kg mass weight 9.81kg on a spring balance. The value of g
ans. 0.981m/sec2
m=10kg
w=9.81kg
w=mg

39. The tendency of  liquid surface to contract is due to the following property
ans. surface tension

40. The surface tension of mercury at normal temperature compared to that of water is
ans. more

41. For very great pressures, viscosity of most gases and liquids
ans. show erratic behaviour

42. A fluid in equilibrium cant sustain
ans. shear stress

43.