ISRO 2017 December Mechanical Questions, Answers and Explanation

ISRO 2017 December Mechanical Questions, Answers and Explanation

Question Set E

1. The specific metal cutting energy is expressed as
a) ^{τ cos(β - α)}⁄_{sin φ cos(φ+β-α)}
b) ^{τ sin(β - α)}⁄_{sin φ cos(φ-β+α)}
c) ^{τ cos(α - β)}⁄_{sin φ cos(φ-β+α)}
d) ^{τ sin(α - β)}⁄_{sin φ cos(φ+β-α)}

where α is rake angle,  β is friction angle, φ is shear angle and  τ is the shear stress.

Answer
a)  ^{τ cos(β - α)}⁄_{sin φ cos(φ+β-α)}

Explanation [Manufacturing Technology]

Specific metal cutting energy is defined as the energy expended in removing a unit volume of work-piece material.
 = Energy/Volume Removed
Energy = Force of cut x velocity of tool
Volume Removed = Velocity of tool x Width of cut x Depth of cut
Specific metal cutting energy = Force of cut/(Width of cut x Depth of cut)
Shear force = shear stress x Area of shear
 = τ x width of cut x depth of cut /sin φ
Shear force/Force of cut = cos(φ+β-α)/cos(β - α)
Force of cut = Shear force x cos(β - α)/cos(φ+β-α)
Specific metal cutting energy = Shear force x cos(β - α)/(cos(φ+β-α)x width of cut x depth of cut x sin φ)
= Shear stress x cos(β - α)/(cos(φ+β-α) x sin φ)
= ^{τ cos(β - α)}⁄_{sin φ cos(φ+β-α)}

2. For isotropic materials, the modulus of Elasticity in tension and shear (E and G) are related to the Poisson's ratio (nu) as follows

a) E = G/(2(1+ν))

b) G = E/(2(1+ν))

c) G = E/(2(1-ν))

d) E = G/(2(1-ν))

Answer
b) G = E/(2(1+ν))

Explanation [Strength of Materials]
Derivation of relation between Modulus of elasticity in tension and shear

3. Which of the following is NOT true?

a) For direct impact of two bodies, coefficient of restitution is the ratio of relative velocity of approach of the two bodies to their relative velocity of separation.

b) Conservation of angular momentum implies that total angular momentum of a system remains constant unless acted on by an external torque

c) Conservation of linear momentum in a given direction implies that the sum of external forces in that direction is zero.

d) The coefficient of friction is independent of area of contact.

Answer
a) For direct impact of two bodies, coefficient of restitution is the ratio of relative velocity of approach of the two bodies to their relative velocity of separation.

Explanation [Engineering Mechanics]
Actually, for direct impact of two bodies, coefficient of restitution is the ratio of relative velocity of separation to the their relative velocity of approach

4. If f(t) = e^at, its Laplace transform (for s > a) is given by
a) ^a⁄_s² + (s-a)

b) ^√π⁄_2(s-a)
c) ¹⁄_(s-a)
d) Does not exist

Answer
c) ¹⁄_(s-a)

Explanation [Engineering Mathematics]
If L{f(t)}=F(s), then L{e^atf(t)}=F(s-a)
In the problem f(t) = 1, L(1) =  F(s) = 1/s
Therefore, L(e^at1) = F(s-a) = 1/(s-a)


5. Smallest thickness which can be measured by a slip gauge is

a) 1.001 mm

b) 0.01 mm

c) 0.001 mm

d) none of these

Answer
a) 1.001 mm

Explanation [Manufacturing Technology]
Slip gauge set of 56 slips is made up as shown below :
9 slips 1.001 to 1.009 in steps of 0.001 mm
9 slips 1.01 to 1.09 in steps of 0.01 mm
9 slips 1.0 to 1.9 in steps of 0.1 mm
25 slips 1 to 25 in steps of 1.0 mm
3 slips 25 to 75 in steps of 25 mm.
From the given choices the smallest thickness that can be measured is 1.001mm and not 0.01mm or 0.001mm.

6. The deflection of an elastic member at the point of application of a force in the direction of that force is given by the derivative of member's total strain energy taken with respect to applied force. This is known as

a) Principle of conservation of strain energy

b) Castigliano's theorem

c) Conservation of momentum

d) Saint-Venant's Principle

Answer
b) Castigliano's theorem

Explanation [Strength of Materials]

There is no such thing as conservation of strain energy. Strain energy acquired by a structure is acquired by the work done due to deflection. 

Castigliano’s first theorem

The first partial derivative of the total internal energy (strain energy) in a structure with respect to any particular deflection component at a point is equal to the force applied at that point and in the direction corresponding to that deflection component.

This first theorem is applicable to linearly or nonlinearly elastic structures in which the temperature is constant and the supports are unyielding.

Castigliano’s second theorem

The first partial derivative of the total internal energy in a structure with respect to the force applied at any point is equal to the deflection at the point of application of that force in the direction of its line of action.

Conservation of momentum does not apply in this case as there is no velocity involved.

Saint-Venant's Principle

If the forces acting on a small portion of the surface of an elastic body are replaced by another statically equivalent system of forces acting on the same portion of the surface, this redistribution of loading produces substantial changes in the stresses locally but has a negligible effect on the stresses at distances which are large in comparison with the linear dimensions of the surface on which the forces are changed. 

7. Thumb rule between feed and nose radius in rough turning is

a) f = 0.3r

b) f = 0.5r

c) f = 0.7r

d) f = 0.9r

Answer
b) f = 0.5r

Explanation [Manufacturing Technology]
Rough turning is the removal of excess stock from a work piece as rapidly and efficiently as possible.
Small nose radius

• Ideal for small cutting depth
• Reduces vibration
• Less insert strength

Large nose radius

• Heavy feed rates
• Large depths of cut
• Strong edge
• Increased radial forces

The radial forces that push the insert away from the cutting surface becomes more axial as the depth of cut increases. It is preferable to have more axial forces instead of radial, which have a negative effects on the cutting action e.g. with more tendencies to vibrate and bad surface finish with increased radial forces.

The nose radius also affects the chip formation. Generally, chip breaking improves with a smaller radius.As a general rule of thumb, the depth of cut should be greater than or equal to 2/3 of the nose radius, or 1/2 of the nose radius in the feed direction.

8. Which of the following is FALSE?

a) A reverted gear train is one in which the first and last gears are on the same axis.

b) Train value for a gear is the ratio of product of driven tooth numbers to product of driving tooth numbers.

c) A planetary gear train is one in which the axes of some of the gears may have a motion.

d) A compound gear train is one which has two or more gears on each axis.

Answer
b) Train value for a gear is the ratio of product of driven tooth numbers to product of driving tooth numbers.

Explanation [Theory of Machines and Mechanical Vibrations]
By definition the axes of first driver and last driven of a reverted gear is co-axial.

Train value of a gear train is the ratio of the speed of the driven gear to the speed of the driving gear. As the speed of a gear is inversely proportional to the number of teeth in it the correct definition of the train ratio is the "ratio of product of driving tooth numbers to the product of the driven tooth numbers".

In a planetary gear train at-least one of the gears revolve around another gear in the gear train.

A compound gear train is one which at-least one pair of gears are rigidly mounted on the same shaft and thus having same revolution speed.

9. Which of the following is true for ductile materials?

a) Engineering stress – strain curve cannot have negative slope

b) Most applicable failure theory is maximum principal stress theory

c) Ultimate strain is the strain at ultimate stress

d) Strain hardening is represented by a negative slope in engineering stress strain curve

Answer
c) Ultimate strain is the strain at ultimate stress

Explanation [Strength of Materials]
Principal stress theory is applicable for brittle materials.

10. Transportation method is concerned with

a) Value analysis

b) Linear programming

c) Queuing theory

d) Break-even analysis

Answer
b) Linear programming

Explanation [Manufacturing Technology]

Value analysis - the systematic and critical assessment by an organization of every feature of a product to ensure that its cost is no greater than is necessary to carry out its functions.

Linear programming - Linear programming is a method to achieve the best outcome in a mathematical model whose requirements are represented by linear relationships.

Queuing theory - Queuing theory is the mathematical study of waiting lines, or queues. A queuing model is constructed so that queue lengths and waiting time can be predicted.

Break-even analysis  - Break-even analysis is a technique widely used by production management and management accountants. ... Total variable and fixed costs are compared with sales revenue in order to determine the level of sales volume, sales value or production at which the business makes neither a profit nor a loss 

Transportation method - The Transportation Method of linear programming is applied to the problems related to the study of the efficient transportation routes i.e. how efficiently the product from different sources of production is transported to the different destinations, such as the total transportation cost is minimum.

11.The reaction in which a liquid phase transform into two different solid phases is called

a) Eutectoid reaction

b) Peritectic reaction

c) Eutectic reaction

d) Peritectoid reaction

Answer
c) Eutectic reaction

Explanation [Material Science]

Eutectoid reaction - This describes the phase transformation of one solid into 2 different solids. In the Fe-C system there is a eutectoid point at approximately 0.8%wt C, 723^oC.

Solid γ gives Solid α + Solid β 

or Austenite gives Ferrite + Cementite

Peritectic reaction - A peritectic reaction is a reaction where a solid phase and liquid phase will together form a second solid phase at a particular temperature and composition

Eutectic reaction - A eutectic reaction is a three-phase reaction, by which, on cooling, a liquid transforms into two solid phases at the same time.

Peritectoid reaction - A type of isothermal reversible reaction in the solid state that results in a new n-1 solid phase from n phases. 

12. Margin wear in drill is due to

a) abrasion

b) vibration

c) thermal softening

d) diffusion

Answer
c) thermal softening


Explanation [Manufacturing Technology]

The margin edge of a drill contacts the drilled hole surface, therefore its wear has a large impact on the hole quality. The only clear sign of margin wear is revealed by lateral vibration at the final stage of the drilling process.

Thermal softening is a heat treatment process; softening processes remove the lattice defects introduced into the aluminium structure during cold working (such as rolling or cold impact extrusion). This also leads to an increase in ductility. In contrast to soft annealing, thermal softening occurs as a temperature below the recrystallisation temperature.

Work-piece material is subjected to work hardening and thermal softening effect during machining, especially at high cutting temperature and pressure. When machining titanium alloys, the hardness just beneath the machined surface was found to be softer than the bulk material hardness due to the thermal softening effect. However, when the depth below the machined surface increases, the hardness value starts to increase before reaching its peak value and finally drops gradually to the bulk material hardness. The increase in hardness value is directly associated with the effect of work hardening. This effect depends on the temperature, cutting time and the mechanism of internal stress relaxation.

Attrition and diffusion are the dominant tool wear mechanisms, especially in the helical flute of drill. With prolonged drilling, these tool wear mechanisms lead to the catastrophic failure of the drill. 

Attrition wear is a removal of grains or agglomerates of tool material by the adherent chip or work-piece. This could be due to intermittent adhesion between the tool and the work-piece as a result of the irregular chip flow and the breaking of a partially stable built-up edge. When seizure between the tool and the work-piece is broken, small fragments of the tool can be plucked out due to weakening of the binder and transported material via the underside of the chip or by the work-piece. The presence of fatigue during machining operation can initiate cracks and also encourage cracks propagation on the tool.

Diffusion wear is associated with the chemical affinity between the tool and work-piece materials under high temperature and pressure during machining of titanium alloys. An intimate contact between the tool work piece interface at temperature above 800º C provides an ideal environment for diffusion of tool material across the tool-work-piece interface. Due to high chemical reactivity of titanium alloys, carbon reacts readily with titanium. Therefore, the formation of titanium carbide occurs at the interface between the tool and work material.

13. The specific speed of the Kaplan turbine is

a) 2.0-5.0

b) < 0.3<0 .3="" 0="" p="">

c) 0.3-2.0

d) none of these

Answer
a) 2.0-5.0

Explanation [Fluid Mechanics]
Dimensionless specific speed range
Pelton wheel - 0.03 to 0.3
Francis turbine - 0.3 to 2
Kaplan turbine - 2 to 5

14. The type of locator used to prevent jamming during locating of a work piece is

a) concentric locator

b) integral locator

c) equilateral locator

d) spherical locator

Answer
d) spherical locator

Explanation
Concentric locators, for the most part, locate a work-piece from a central axis. This axis may or may not be in the center of the work-piece. 

15. A carton carrying vessel of mass 10 tons (width = length = 5m, height = 6m), floats on water. The mass of contents of the vessel are symmetrically placed. If the vessel tilts by 0.01 radians by moving a 50kg carton from the centre by a distance of 2m towards side in horizontal direction, the metacentric height of the vessel is (g = 10m/s²)

a) 1m

b) 3m

c) 1.5m

d) 2m

Answer
a) 1m

17. Which if the following is TRUE for vibration of a mechanical system

a) Damping ratio is the ratio of the critical damping to the actual damping

b) The damping can be obtained from the response of the system under forced vibration using logarithmic decrement method.

c) For damped mechanical systems, the amplitude of vibration tends to become infinity when excitation frequency reaches the system's natural frequency

d) Amplitude ratio and transmissibility of a vibration isolator is unity when the frequency of exciting force is sqrt(2) times the natural frequency.

Answer
d)

18. What is the maximum rate that a heat pump which uses 1kW of electric power can supply heat to a house at 27C when the outside temperature is 12C

a) 50J/s

b) 25kJ/s

c) 20kJ/s

d) 30J/s

Answer
c) 20kJ/s

Explanation [Thermal Engineering]
At maximum efficiency, Q₂/Q₁ = T₂/T₁
Q₂/Q₁ = T₂/T₁=300/285, Q₁=285Q₂/300
Q₁+W=Q₂
W = 15/300 Q₂
Q₂ = 20*1kJ/s = 20kJ/s

20. White iron structure consists of

a) Pearlite

b) Cementite

c) Ferrite

d) Pearlite and Cementite

Answer
d) Pearlite and Cementite
Other Manufacturing Technology Questions

23. A man draws 3 balls from a jug containing 5 white balls and 7 black balls. He gets Rs. 20 for each white ball and Rs. 10 for each black ball. What is his expectation?

a) Rs. 21.25

b) Rs 42.50

c) Rs 31.50

d) Rs 45.21

Answer
b) Rs 42.50

Explanation [Engineering Mathematics]
3 balls can be drawn in the following ways
- 3 white balls, P = 5C3/11C3 = 10/220 = 2/44
- 2 white balls and 1 black ball, P = 5C2*7C1/11C3 = 70/220 = 14/44
- 1 white ball and 2 black balls, P = 5C1*7C2/11C3 = 125/220 = 21/44
- 3 black balls, P = 7C3/11C3 = 35/220 = 7/44
Expectation = sum of the product of probability and the money he gets for each combination
= (2/44)*60 + (14/44)*50 + (21/44)*40 + (7/44)*30 = 935/22 = 85/2 = 42.50

27. Arrange the metals Aluminium, Copper, Iron & Silver in increasing order of thermal conductivity

a) Iron, Aluminium, Copper, Silver

b) Aluminium, Iron, Copper, Silver

c) Copper, Iron, Silver, Aluminium

d) Iron, Copper, Aluminium, Silver

Answer
a) Iron Aluminium, Copper, Silver

Explanation [Material Science]
Thermal conductivity of Silver - 406 W/mK
Thermal conductivity of Copper - 385 W/mK
Thermal conductivity of Aluminium - 205 W/mK
Thermal conductivity of Iron - 79.5 W/mK

29. Which of the following is FALSE?

a) Heat flow by conduction is directly proportional to the area and temperature gradient

b) Heat flow by convection is directly proportional to the area and temperature difference

c) Heat flow by radiation is directly proportional to the cube of absolute temperature of the radiating body

d) Emissivity of perfect black body is unity

Answer
c)

Explanation [Heat Transfer]
Heat flow by radiation is directly proportional to the fourth power of absolute temperature of the radiating body.

30. The most applicable failure theory for metals like Aluminium is

a) Maximum principal stress theory

b) Maximum principal strain theory

c) Total strain energy theory

d) Maximum distortion energy theory

Answer
d) Maximum distortion energy theory

31. Which one of the following is FALSE?

a) Number of Taps generally used for hand tapping is 3

b) Piispanen's model in machining is used to estimate shear strain

c) Chip hammering during machining is due to improper chip control

d) Cemented carbide tools are generally poor in compression

Answer
d)

32. A statistical process control chart which shows the number of defects found in a subgroup of fixed size is

a) C-chart

b) R-chart

c) Control chart

d) Gantt chart

Answer
a) C-chart

33. Complex irregular three dimensional surfaces can be located using the following method

a) Sighting

b) Nesting

c) Integral locators

d) Buttons

Answer
b) Nesting

36. A point P moves along the path y = x² -4. What is the displacement when the point moves from x =1 to x = 3.
a) 8.24, @ tan^-1 (4)
b) 2,  @ tan^-1 (1)
c) 11.3, @ tan^-1 (4)
d) 11.3,  @ tan^-1 (1)

Answer
a) 8.24, @ tan^-1 (4)

Explanation [Engineering Mathematics]
when x = 1, y = 1-4 = -3
when x = 3, y = 9-4 = 5
distance between the 2 points = √ (2²+8²) = √ (68), which is just greater than 8. So other options are eliminated.

38. Identify the geometric characteristic that describe the feature geometry and the inter-relationship of part features

a) form tolerance

b) form

c) orientation tolerance

d) dimension

Answer
b) form

39. Isothermal compressibility of an ideal gas is
a) nR/VP
b) nRT/VP²
c) nR/VP²
d) nRT/VP

Answer
b) nRT/VP²

Explanation [Thermal Engineering]
Compressibility is the inverse of bulk modulus
Bulk modulus is the ratio change in pressure to strain = -dP/(dV/V)
Therefore, compressibility = -dV/(VdP)

For an ideal gas PV = nRT
Since the process is isothermal dT = 0, only differentiable variables are P and V
V = nRT/P
Differentiating dV = -nRTdP/P²
Compressibility = -dV/(VdP) = nRT/VP²

40. Datum features on the part are

a) permanent

b) temporary

c) either permanent or temporary

d) none of these

Answer
c) either permanent or temporary

43. Efficiency of gas turbines lies between

a) 85 to 95%

b) 50 to 60%

c) 30 to 50%

d) 15 to 18%

Answer
d) 15 to 18%

44. Which of the following is impulse turbine?

a) Francis turbine

b) Kaplan turbine

c) Pelton turbine

d) none of these

Answer
c) Pelton turbine

Explanation [Fluid Mechanics]
Impulse Turbine - The whole pressure energy is transformed to kinetic energy. Eg. Pelton turbine
Reaction Turbine - All pressure energy is not transformed into kinetic energy. Eg. Francis, Kaplan turbine

45. Which of the following is FALSE for bolted joints?

a) Bolted joints are preloaded to avoid vibration loosening

b) Threads made by thread rolling process are preferred over machined threads in bolts

c) When external load is applied to preloaded bolt joint, a bigger percentage of that load relieves compression of flanges and remaining percentage increases tension in bolts

d) Bolted joints are designed such that bolt stiffness is higher than flange stiffness

Answer
d)

46. Root opening of a Single Vee groove weld joint of plate thickness “t” is

a) t/3

b) t/4

c) t/5

d) t/6

Answer
b) t/4

47. A cubic B-spline curve requires minimum ......... control points

a) 3

b) 4

c) 5

d) 6

Answer
b) 4

Explanation [Engineering Mathematics]
A line (linear curve) requires minimum 2 control points
A quadratic curve requires minimum 3 control points
In general a curve of degree n requires minimum n+1 control points

48. Which one of the following is FALSE about Boronizing process?

a) it is a pack cementation process

b) it can be done only on high carbon steels

c) it is used to obtain extremely high wear resistant surfaces on steels

d) it leads to high distortion

Answer
b)

Other Manufacturing Technology Questions

49. In dynamic balancing of machines, which of the following is NOT a method of measuring the magnitude and location of correction weight for a two plane correction?

a) Pivoted cradle method

b) Mechanical compensation method

c) Pivoted compensation method

d) Nodal point method

Answer
c)

51. The critical pressure ratio for maximum discharge in steam nozzle is
a) 2⁄γ+1
b) (2⁄(γ+1))^γ
c) (2/(γ+1))^γ-1
d) (2/(γ+1))^γ/(γ-1)

Answer
d) (2/(γ+1))^γ/(γ-1)

Explanation [Thermal Engineering]
Derivation of critical pressure ratio for maximum discharge

52. A jet engine consumes 1kg of fuel for each 40kg of air intake. Fuel consumption is 1kg/sec. When aircraft travels in still air at 200m/sec, velocity of discharge of gases with respect to engine is 700m/sec. The power developed by engine is

a) 7200kW

b) 5600kW

c) 2070kW

d)4140kW

Answer
d) 4140kW

Explanation [Thermal Engineering]
Power developed = Thrust* velocity
A jet engine derives its thrust from compressing incoming air and then mix it with fuel to burn it and then exhausting the hot gases at high velocities through a nozzle.
Thrust = Rate of change of momentum of incoming gases and exhaust gases
Inlet momentum = 40*200 kgm/s
Outlet momentum = (40+1)*700 kgm/s
Power developed = (41*700 - 40*200)*200 = 4140kW

53. Which of the following is most appropriate for various power cycles?

a) In Carnot cycle, expansion of vapour occurs without change in entropy

b) In Rankine cycle, transformation of liquid water in steam generator occurs at constant temperature

c) In Carnot cycle, heating of vapor occurs at constant volume

d) In Rankine cycle, entropy of vapor increases during its expansion in steam turbine

Answer
a) In Carnot cycle, expansion of vapour occurs without change in entropy

Explanation [Thermal Engineering]
Carnot cycle
1. Isothermal compression
2. Isentropic compression
3. Isothermal expansion
4. Isentropic expansion
1 and 2 rules out choice c)
Rankine cycle
1. Isentropic compression
2. Constant pressure heat addition (choice b) ruled out)
3. Isentropic expansion (choice d) ruled out)
4. Constant pressure heat rejection

55. The reheat factor R_f for a steam turbine is usually in the range of

a) 0 to 1

b) 1 to 1.065

c) 2 to 2.065

d) 5 to 10

Answer
b) 1 to 1.065

Explanation [Thermal Engineering]
Reheat factor is the ratio of cumulative heat drop to direct isentropic or Rankine heat drop. It is always greater than 1. 

57. In tolerancing of a part, unless otherwise specified, individual features of size must

a) not violate size limits of MMC at any cross section

b) not violate an envelope of perfect form at LMC

c) not violate an envelope of perfect form at MMC

d) none of these

Answer
c)

59. In CAD, the geometric transformation is expressed as P* = [T]P where T is transformation matrix. If the matrix T is diagonal, then the transformation is called

a) translation

b) reflection

c) rotation

d) scaling

Answer
d) scaling

Explanation
Consider T as 2*2 diagonal matrix with diagonal elements a,b
Let P = [[u,v],[y,z]]
P* = [[au,bv],[ay,bz]] which implies P has scaled

60. A water tank is located 3m above ground and depth of water in tank is 2m. Exit pipe is 50mm in dia and 50 m long. Velocity of water at the exit at the ground level is approximately (Take friction factor f = 0.05, g = 10m/s^2)

a) 1.5m/s

b) 2m/s

c) 0.7m/s

d) 1/4 m/s

Answer
c) 0.7m/s

61. The work ratio of a gas turbine is a function of

a) temperature ratio and pressure ratio

b) pressure ratio

c) temperature ratio

d) none of these

Answer
a) temperature ratio and pressure ratio

62. The distribution of a temperature T, at a particular instant , across a large concrete wall, 1m thick, which is heated from one side is given by the equation T = 150-80x+16x², where the distance x is in meters and T is in degree Celsius. Thermal conductivity of wall is 0.6W/mK, area of cross section is 10 m². The heat accumulated in unit time at this instant in the concrete wall is

a) 768J/sec

b) 384J/sec

c) 96J/sec

d) 192J/sec

Answer
d) 192J/sec

Explanation [Heat Transfer]
Heat accumulated = Heat conducted away - Heat conducted in
Q = kA*[dT/dx] at x = 1 minus at at x = 0
= 0.6*10*(-80+32x) at x = 1 minus at x = 0
=6*32 = 192J/sec

63. Which of the following is the permanent mould casting process?

a) Investment casting process

b) Full mould process

c) Vacuum casting process

d) Die casting process

Answer
d) Die casting process

64. Tolerances generally followed for tooling design are

a) 5-10% of work piece tolerance

b) 11-30% of work piece tolerance

c) 31-50% of work piece tolerance

d) none of these

Answer
c) 31-50%  of work piece tolerance
Other Manufacturing Technology Questions

65. Which of the following is FALSE about Normal distribution

a) Normal Distribution is applied for discrete Random Distribution

b) The shape of the Normal Curve is Bell Shaped

c) The area under a standard normal curve is 1

d) The standard normal curve is symmetric about the value 0

Answer
a)

Explanation
The normal distribution is a commonly encountered continuous probability distribution.
Normal curve is also called "Bell Curve" as it is Bell Shaped.
Area under the standard normal curve is 1.
The standard normal curve is symmetric about the value 0.

66. The temperature of the products of combustion when the maximum amount of chemical energy is converted to thermal energy is

a) Higher than adiabatic flame temperature

b) Lower than adiabatic flame temperature

c) Equal to adiabatic flame temperature

d) Independent of adiabatic flame temperature

Answer
c) Equal to adiabatic flame temperature

Explanation [Thermal Engineering]

Maximum amount of chemical energy is converted to thermal energy when the air fuel ratio is stoichiometric. At that ratio, the adiabatic flame temperature is equal to the temperature of the products of combustion. 
When the air fuel ratio is less or more the temperature of products of combustion is always less than the adiabatic flame temperature.

67. Frederic W Taylor introduced a system of working known as

a) line organisation

b) effective organisation

c) functional organisation

d) none of the above

Answer
c) functional organisation

68. Adaptive response rate forecasting is related to

a) Production Planning

b) Production Scheduling

c) Value analysis

d) Inventory control

Answer
d) Inventory control

69. Process in which lowest tolerances in cast products of ferrous and non ferrous metals can be achieved is

a) Die casting

b) Shell casting

c) Investment casting

d) Sand casting

Answer
c) Investment casting

Other Manufacturing Technology Questions

70. Pickling treatment is cleaning the casting with

a) Soda ash

b) Dilute acid

c) Compressed air and sand particles

d) Iron shots

Answer
b) Dilute acid
Other Manufacturing Technology Questions

Explanation
Pickling is removal of scale by chemical means.

71. Element which makes steel stainless

a) Mg

b) Ni

c) C

d) Cr

Answer
d) Cr

Explanation [Material Science]

Chromium is the dominant other metal present in stainless steel (> 10%). It helps forming a very thin stable film of its oxide and hydroxide which limits additional corrosion and is not visible contrary to Iron oxides and hydroxides.

Nickel - Increases strength and hardness without sacrificing ductility and toughness. It also increases resistance to corrosion and scaling at elevated temperatures when introduced in suitable quantities in high-chromium (stainless) steels.

Carbon - The most important constituent of steel. It raises tensile strength, hardness, and resistance to wear and abrasion. It lowers ductility, toughness and machinability.

Magnesium - Magnesium is not used in stainless steel. Magnesium - iron alloys are used to make electrochemical heat sources.

72. Isentropic process is related to

a) Adiabatic Expansion

b) Reversible Adiabatic Expansion

c) Isothermal Expansion

d) Reversible Isothermal Expansion

Answer
b) Reversible Adiabatic Expansion

Explanation [Thermal Engineering]

Irreversible free expansion of a gas in adiabatic condition is not isentropic. There is an increase of entropy. The equation of dS=dQ/T is not an accurate equation, the actual equation should be dS=dQ_reversible/T. For dQ of irreversible the equation should be changed into the clausius inequality form which is dS> dQ _irreversibl/T. Under this clausius inequality equation, even dQ is zero in the adiabatic condition, and the right hand side equation is equal to zero, the left side dS is greater than zero which means that the dS entropy is increasing.

An isentropic process is an idealized thermodynamic process that is both adiabatic and reversible. The work transfers of the system are frictionless, and there is no transfer of heat or matter.

In reversible isothermal process the entropy change of the universe is zero. But as temperature of the system remains constant, there is net heat flow into the system thereby increasing the entropy of the system.

In an isothermal expansion there is net increase in entropy as explained before because entropy is a state property

74. Isochoric changes in ideal gas are characterized by

a) V/T = Const

b) PV = Const

c) P/T = Const

d) None of these

Answer
c) P/T = Const

Explanation [Thermal Engineering]
For an isochoric process volume remains constant, therefore PV = nRT reduces to P/T = constant

75. A cantilever beam of cross section area 'A', moment of Inertia 'I' and length 'L' is having natural frequency ω₁. If the beam is accidentally broken into two halves, the natural frequency of the remaining cantilever beam ω₂ will be such that

a) ω₂

b) ω₂> ω₁

c) ω₂=ω₁

d) Cannot be obtained from the given data

Answer
b) ω₂> ω₁

Explanation [Theory of Machines and Mechanical Vibrations]
The natural frequency ω_n ∝ 1/L² √ (EI/ρA)
So when the length is halved the natural frequency quadruples.

76. A 3m long steel shaft has to transmit 7.5kW at 3600rpm. Required shaft diameter is given by(Take allowable shear stress = 100N/mm², π² = 10)?

a) 10mm

b) 7.5mm

c) 25mm

d) 12.5mm

Answer
a) 10mm

Explanation [Strength of Materials]
From the torsion theory 
T/I_p = τ/r
and 
P = 2πNT/60
where
T - Torque
I_p - polar moment of inertia = π d⁴/32
τ - shear stress
r - radius where shear stress is measured
P - power transmitted
N - revolutions per minute
Maximum shear stress occurs at r = d/2

Combining the 2 equations
P = 2πN/60 *2 I_pτ/d
P = πNπ d⁴τ/(15*32d)
d³ = 15*32*P/(π²Nτ)
   = 15*32*7500/(10*3600*100*10⁶)
   = 0.000001
d = 0.01m = 10mm

77. For thin cylindrical shell structures loaded in compression, the design is based on

a) Yield strength of material

b) Ultimate strength of material

c) Buckling strength of the structure

d) Shear strength of the structure

Answer
c) Buckling stress of the structure.

Explanation [Strength of Materials]
Yield strength is the point where the material tends to deform. For the structures that should not deform on usage, the design is based on yield strength of material.
Brittle materials generally fails at the ultimate strength of material.
Buckling under axial compression is normally the controlling design consideration for thin cylindrical structures. Thin and long cylindrical structures fail before the yield strength of the member is reached. 
Shear strength of a component is important for designing the dimensions and materials to be used for the manufacture or construction of the component e.g. beams, plates, or bolts

80.  A point moves according to the relation x = 8t² cos ω t , y = -4t³ sin ωt, where x and y are in meters and t in seconds. If angular velocity ω = 8 π rad/s, velocity vector of the point at t = 0.5s is given by
a) 8 + j4π
b) 6 + j20π
c) 8 - j4π
d) -20π -j6

Answer
c) 8 - j4π

Explanation [Engineering Mathematics]
x = 8t² cos ω t
y = -4t³ sin ωt

u = dx/dt = 16t cos ω t - 8ωt² sin ω t
v = dy/dt = -12t² sin ωt - -4ωt³ cos ωt

velocity vector = u + jv

 = 16t cos ω t - 8ωt² sin ω t + j(-12t² sin ωt - 4ωt³ cos ωt)
Substituting ω = 8 π rad/s and t = 0.5s,
velocity vector = 16*0.5 cos 8 π *0.5 - 8*8 π*0.5² sin 8 π *0.5 + j(-12*0.5² sin 8 π*0.5 -4*8 π*0.5³ cos 8 π*0.5)

 = 8 cos 4 π  - 2 sin 4 π + j(-3 sin 4 π -4 πcos 4 π)

 = 8 - j4 π

Further Reading

• ISRO 2017 May Mechanical Questions, Answers and Explanation
• ISRO Previous Years (2007 to 2016) Mechanical Questions, Answers and Explanation
• ISRO 2006 Mechanical Questions, Answers and Explanation
• ISRO Mechanical - Engineering Mathematics Questions, Answers and Explanation,
• ISRO Mechanical Manufacturing Technology Questions, Answers and Explanation