Some basics which you have to know






1. What is the difference between Pipe and Tube?
Ex. Iron Pipe, Carbon Tube, Steel Tube etc.
· Tube is defined by Outer diameter and Wall thickness (OD and WT). While Pipe is defined by Inner diameter (ID).
Example:
2 inch pipe have 2.375 inch outer diameter, where 2 inch tube have same 2 inch outer diameter.
· Tube is easily shaped by bending, where Pipe needs some mechanical work to shape it.
· Tube is tight then Pipe.
· Tube is applicable to non cylindrical sections like Square and Rectangular.

2. Is gate valve used for Throttling?
Gate valves are not suitable for throttling because the control of flow is difficult for the  valve’s  design,  and  the  flow  of  fluid slapping   against   a   partially   open   gate   can cause  extensive  damage  to  the  valve.

3. Why is the Suction pipe of Vapour Compression Refrigeration system insulated?
1. It prevents the suction line from sweating and dripping water inside the house.
2. The insulation also prevents the suction line attracting heat from the outdoors on its way to the condenser coil.

4. How does Welding damage Eye sight?
An Electric welding arc produces Ultraviolet light and the UV light (Sun burn) will damage the retina. Welding shields or Goggles with the proper shade (Automatic shading) of lens is the best protection for welders.
Light filtering curtains and reduced reflective surfaces help protect both welders and observers in the area.

5. Explain why BCC, FCC and CPH lattice packing and features of grain structure affect the Ductility and Brittleness of parent metallic materials?
Ductility is the mechanical property of a material. (It is the material’s ability to deform under the tensile stress without fracture). So it is depends on the atoms how they arranged in a lattice and its grain size. The ability to absorb the energy of the impact and fracture resistance depends on the arrangement of the atoms in a lattice and features of grain structure.

6. Why do you have Truss Bridges?
Truss bridges carry load in tension and compression rather than bending (Self weight + The weight of vehicles crossing it + Wind loads). A truss has the ability to dissipate a load through the truss work. The beams are usually arranged in a repeated triangular pattern, since a triangle cannot be distorted by stress.

7. Why I-section beam is preferred for heavy loading?
Cross sectional shape I, giving many benefits. It is very good for giving stiffness (less deformation on loading) and to withstand higher bending moments (as a result of heavy loading) on comparison with other cross-sectional shapes of same area. Also, it is very easy to manufacture. It will have more moment of inertia.

8. What is difference between Center of Mass and Center of Gravity?
Both terms are same when gravity is uniform. When gravity is non-uniform following are the terms:
The center of mass is a point that acts as if all the mass was centered there (the mass on one side of the point is equal to the mass on the opposite side). If supported at the center of mass, an object will be balanced under the influence of gravity.
The center of gravity is the point at which where the sum (vector) of the gravitational forces act on an object which will be balanced on that point.

9. What is the difference between Center of Mass and Centroid?
If the material composing a body is uniform or homogeneous, the density or specific weight will be constant throughout the body, and then the centroid is the same as the center of gravity or center of mass.
Centroid: Centroid is the point, where the whole area of plane is going to be act. It is valid only for 2D problems like plane figures, square plate etc.
The center of mass is a point that acts as if all the mass was centered there (the mass on one side of the point is equal to the mass on the OPPOSITE side). If supported at the center of mass, an object will be balanced under the influence of gravity.

10. What are the differences between Weight and Mass?
Mass is a measure of how much matter an object has. Mass is specified in Gram or Kilograms.
Weight is a measure of how strongly gravity pulls on that matter. Force is measured in Newton’s.
F=m.g
Thus if you were to travel to the moon your weight would change because the pull of gravity is weaker there than on Earth but, your mass would stay the same because you are still made up of the same amount of matter.

11. What is the difference between Projectile motion and a Rocket motion?
A projectile has no motor/rocket on it, so all of its momentum is given to it as it is launched. An example of a projectile would be 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.
In mechanics point of view projectile don’t have any particular shape it is a point mass. Whereas rocket has a particular shape and hence it has center of gravity situated at particular point on its body. Therefore rocket motion comes under kinetics and projectile comes under kinematics.

12. What type of cooling used in High Voltage Transformer?
The big transformers you find on power poles usually use oil as a dielectric insulator, in smaller HV transformers, like the ones in TV’s are usually filled with resin.

13. What is honing of Cylinder Liners?
The honing equipment used has been manufactured by "Chris Marine". The head of the honing device consists of four synchronized stones. For the initial honing diamond stones are used to break up the hardened surface in the scuffed areas. For the main honing very coarse and hard stones are used to produce a very desirable rough surface all over the liner.
The advantage, especially for the 2-stroke engines, is possibility to save the liner after a seizure, scuffing or blow-by or even to eliminate the ovality of the liner. Another advantage is that it is possible to machine a rough liner wall to obtain a well oiled surface.

14. What is the difference between Speed and Velocity?
Speed is scalar quantity and Velocity is a vector – velocity has both speed and direction.
Speed is expressed as distance moved (d) per unit of time(t). Speed is measured in the same physical units of measurement as velocity, but does not contain an element of direction. Speed is thus the magnitude component of velocity.
15. Difference between Yield Stress and Yield Strength?
Stress is a measure of the load applied to a sample relative to a cross sectional area of the sample. Strength is a quantification of the samples ability to carry a load. The terms "yield strength" and "yield stress" of a material are usually used interchangeably (correct or not). It is the stress which will just cause the material to plastically deform. If a material yields at 30,000 psi, the yield stress is 30,000 psi. If the part in question has a cross sectional area of 2 square inches, the strength at yield would be 60,000 pounds, but usually we just say the yield strength is 30,000 psi.

16. What is the difference between Yield and Ultimate tensile strength?
The yield strength is reached when the material becomes Non – linear (that is non elastic) and takes a permanent set when load is released. Material stretches but does not break. Ultimate strength is when it breaks and is higher than yield strength.

17. What is the difference between Flexural strength and Tensile strength?
Flexural strength is resistance offered against bending. Tensile strength is resistance offered against tensile force.

18. What is the difference between Shear and Tensile strength?
Tensile Strength for a Bolt is determined by applying a Force along it long axis. Shear Strength for a Bolt is determined by applying a Force across its diameter, as it would be loaded in a lug joint. Tensile strength is strength in tension when pulling force is applied. And shear strength is strength against cutting force which is known as shear force.

19. What is the difference between Tensile strength and Tensile modulus?
Tensile strength is the ultimate capacity of the material to resist a tensile load regardless of deflection.
Tensile modulus also known as Young’s modulus is a measure of the stiffness of an isotropic elastic material. It is defined as the ratio of the uni-axial stress over the uni-axial strain. It is determined from the slope of a stress-strain curve traced during tensile tests conducted on a sample of the material.
(1) Pitot tube is used for measurement of
(a) Pressure
(b) Temperature
(c) Discharge
(d) Velocity
Ans.: (d) Velocity

(2) Slow plastic deformation of material under constant stress is
(a) Creep
(b) Fatigue
(c) Endurance
(d) Elastic deformation
Ans.: (a) Creep

(3) Mass balancing is done to
(a) Avoid flutter
(b) Increase bending stress
(c) Reduce drag
(d) Distributing mass on control surface
Ans.: (a) Avoid flutter

(4) Short columns are preferred over long columns from
(a) Strength consideration
(b) Buckling consideration
(c) Weight consideration
(d) None of the above
Ans.: (b) Buckling consideration

(5) Centre of pressure of an aerofoil with an increase of angle of attack will
(a) Move forward
(b) Move backward
(c) Not move
(d) None of the above
Ans.: (a) Move forward

(6) Thermal efficiency of a gas turbine plant as compared to diesel engine plant
(a) Higher
(b) Lower
(c) Same
(d) May be higher or lower
Ans.: (a) Higher

(7) A closed cycle gas turbine works on
(a) Carnot cycle
(b) Rankine cycle
(c) Joule cycle
(d) Atkinson cycle
Ans.: (c) Joule cycle

(8) A bolt of uniform strength can be developed by
(a) Keeping the core dia of threads equal to the dia of unthreaded portion of bolt
(b) Keeping the core dia of threads smaller than the dia of unthreaded portion of bolt
(c) Keeping the nominal dia of threads equal to the dia of unthreaded portion of bolt
(d) None of the above
Ans.: (a) Keeping the core dia of threads equal to the dia of unthreaded portion of bolt
(9) Stress concentration factor is defined as ratio of
(a) Max stress to endurance limit
(b) Nominal stress to endurance limit
(c) Max stress to nominal stress
(d) Nominal stress to max stress
Ans.: (c) Max stress to nominal stress

(10) Principle effect of humidity is
(a) Corrosion
(b) Leaking from sealed enclosures
(c) Permanent set of packing and gaskets
(d) Differential contraction of metal parts
Ans.: (a) Corrosion

(11) Backlash is
(a) Sum of the clearance of two gears
(b) Mutual play between two gears
(c) Amount by which the width of a tooth space exceeds the thickness of the engaging tooth on pitch circle
(d) Any of the above
Ans.: (c) Amount by which the width of a tooth space exceeds the thickness of the engaging tooth on pitch circle

(12) Teflon is used for bearings because of
(a) Low co-efficient of friction
(b) Better heat dissipation
(c) Smaller space constraint
(d) All of the above
Ans.: (a) Low co-efficient of friction

(13) When two elastic bodies collide with each other
(a) Two bodies will momentarily come to rest after collision
(b) The two bodies tend to compress & deform at the surface of contact
(c) Two bodies begins to retain their original shape
(d) All of the above
Ans.: (d) All of the above

(14) Antifriction bearings are
(a) Thick lubricated bearing
(b) Thin lubricated bearing
(c) Ball & roller bearing
(d) Plastic bearing
Ans.: (c) Ball & roller bearing

(15) What is Hertzian stress?
(a) Tensile stress on inner surface of cylinder
(b) Bending stress on two contact surface
(c) Contact stress on two contact surfaces
(d) Shear stress on two contact surfaces
Ans.: (c) Contact stress on two contact surfaces
(16) Mohr’s circle can be used to determine following stress on inclined surface
(a) Principal stresses
(b) Normal stresses
(c) Maximum shear stresses
(d) All of the above
Ans.: (a) Principal stresses

(17) What size of material required for making rolled threads?
(a) Pitch diameter
(b) Root diameter
(c) Major diameter
(d) None
Ans.: (a) Pitch diameter









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