ARUNACHAL PRADESH PUBLIC SERVICE COMMISSION ITANAGAR
SUBJECT: MECHANICAL ENCINEERINC PAPER
Time: 3 hours Full Marks: 200
Note: Answer Question No.1 and any four from the rest. All questions carry equal marks.
Q. No.1. Attempt any 10 10 x4 =40
a.
What is the function of a governor? How is it different from a flywheel?

b.
What is a gear train? Give its classification.

c.
Derive an expression for the length of open flat belt in terms of diameters of pulleys and centre distance.

d.
What are the advantages of welding joints over riveted joints?

e.
Draw a sleeve or Muff coupling showing important dimensions.

f.
What are the primary functions of springs?

g.
Give the important theories of failures as applied in machine design.

h.
What is an alloy? Why is an alloy preferable to pure metal?

i.
Differentiate between quenching and normalizing.

j.
Why are discontinuous type chips preferred over continuous type?

k.
What are the requirements of a tool material to get a reasonable tool life?

I.
What are the basic differences between PERT and


Q. No. 2 Attempt any 8 (eight) 8 xS =40
a.
Give briefly the classification of followers with examples.

b.
Explain how the balancing of a revolving disturbing weight is done by a balanced weight in different planes parallel to the plane of rotation of the disturbing weight.

c.
What do you mean damping in mechanical vibrations?

d.
State the classification of shafts.

e.
Differentiate between Hydrostatic bearing and Hydrodynamic bearing.

f.
Define Principal stress and Oi) Principal planes


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g.
Give the construction of Mohr's circle for biaxial stress

h.
Give the Eutectoid reaction at the Eutectoid temperature.

i.
What are the advantages of plastic materials?

j.
Explain different types of weld joints with neat sketches.


Q. No.3 Attempt any 5 (five) 5 x 8 =40
a.
Define in case of a governor Sensitiveness, Isochronism

b.
Differentiate free vibrations and forced vibrations.

c.
Show that for a belt drive, the ratio of belt tensions is given by
/1.8



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d.
Derive an expression for the maximum bending moment of a cantilever beam subjected to uniformly distributed loading of intensity woo

e.
Diameter of a water supply pipe is 700 mm. It has to stand a water head of 60 m. If the permissible stress of the material is 20 MPa, find out the required thickness of the pipe. Consider the specific weight of water to be 9810 N/m3.

f.
For a cantilever beam of length find out the maximum deflection of the beam due to a concentrated load acting at the free end. Assume constant

g.
What are the advantages of CNC system over conventional NC system.


Q.No.4 Attempt any 4 (four) 4 x 10 40
a.
Four masses A =200 kg, B =300 kg, C =240 kgand D =260 kg are with the radii of rotation rl =20 em, r2 =15 em, r3 =25emand r4 =30 em respectively. The masses are at an angle of 75° and 135° with the mass A respectively. Find the position and magnitude of the balance mass required if the radius of rotation is 20 em.

b.
A plate 75 mm wide and 12.5 mm thick is joined with another plate by a single transverse


,weld and a double parallel weld as shown in fig 4b. The maximum tensile and shear stress are 70 MPa and 56 MPa respectively. Find the length of each parallel fillet weld if the joint, is subjected to static loading.

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Fig 4b
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c.
A close-coiled helical spring has stiffness 900 N/m in compression with a maximum load of 45 N and maximum shear stress of 120 N/mm2. The solid length of the spring is 45 mm. Find out wire diameter, mean coil radius and number of coils. Take G =0.4 X 105 N/mm2•

d.
A solid circular shaft is subjected to an axial tensile force 27 kN and a bending moment 3165 Nm. Based on an allowable tensile stress of 120 MPa, calculate the required shaft diameter.

e.
Direct tensile stress of 120 MPa and 70 MPa act on a body on mutually perpendicular planes. What is the magnitude of shearing stress that can be applied so that major principal stress at the point does not exceed 135 MPa? Determine the value of major principal stress and the maximum shear stress.


Q.No.5 Attempt any 2 2 x 20 =40
a. What is meant by effort and power of a governor? Find the expression for effort in a Porter governor. The arms of a Porter governor are each 200 mm long and pivoted on the axis of rotation. Weight of each ball is 40 N and that of the sleeve is 200 N. The radius of rotation of the balls is 125 mm when the sleeve begins to rise and reaches a value of 150 mm for maximum speed. Find the speed range of the governor.
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b.
Sketch a spur gear and show the follOWing: face, flank, top land, bottom land, addendum and dedendum. In an epicyclic gear train, an arm carries two gears A and B having 36 and 45 teeth respectively. If the arm rotates at 150 rpm in counter clockwise direction about the centre of the gear A which is fixed, determine the speed of the gear B. If the gear A instead of being fixed makes 250 rpm in the clockwise direction, what will be the speed of gear +14

c.
What is meant by and 'structure' of a grinding wheel? Sketch and explain the three methods of external centre-less grinding.


Q.No.6 Attempt any 4 (four) 4x 10 =40
a.
Discuss with neat sketches the different types of chip breakers. How does chip breakers increase tool life?

b.
Discuss the different types of welding equipment used in gas welding.

c.
What is a core? What is its use? Give the characteristics of a good core.

d.
How is cold rolling done? What benefits are obtained from cold rolling metal? Why for cold rolling, a four high mill is usually used?

e.
Enumerate the essential requirements of a cutting tool material. Discuss the role of carbon, chromium, manganese, molybdenum, cobalt, vanadium and tungsten in toolsteels.


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Q.No.7 Attempt any 2 2 x 20 =40
a.
Design a belt drive to transmit 110 kW for a system consisting of two pulleys of diameters 0.9 m and 1.2 centre distance 3.6 a belt speed 20 mis, coefficient of friction 0.3, a slip of 1.2% at each pulley and friction loss at each shaft, 20% overload.

b.
Establish a relationship for stiffness of a close coil helical spring having coil diameter wire diameter and number of coil A closed coil helical spring has coil diameter to wire diameter ratio of 6. The spring deflects 4


cm under a load of 60 N and maximum shear stress produced in the wire of spring is 125 N/mm2• Determine the diameter of the wire, number of coils required, length of the wire.
c. The effective turning moment exerted by two stroke engine at crank shaft is represented by:(cycle repeats every 1800 of crank rotation)
T =800 100 Sin 28 -200 Cos 28 Where 8 =inclination of the crank to the inner dead centre. The weight of flywheel is 5 kN and its radius of gyration is 750 mm. The engine speed is 300 rpm. Assuming external resistance as constant, determine

power developed,


the total percentage fluctuation of speed.


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