Solved Question Paper for Foreman (Mechanical) in Ministry of Defence, Junior Scientific Officer (Mechanical) in Ministry of Defence, Assistant Executive Engineer (Mechanical), Additional Assistant Director (Safety) (Mechanical), Senior Scientific Assistant (Mechanical), Ministry of Defence & Junior Works Manager (Mechanical), Ministry of Defence conducted by UPSC

71. Statement (I): When variables are a few, then Rayleigh method is used in dimensional analysis.

Statement (II): When variables are more, then Buckingham π-method is used since the Rayleigh method becomes cumbersome in dimensional analysis.

(a) Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I)

(b) Both Statement (I) and Statement (II) are individually true but Statement (II) is NOT the correct explanation of Statement (I)

(c) Statement (I) is true but Statement (II) is false

(d) Statement (I) is false but Statement (II) is true

Answer: (a)

72. Consider the following assumptions made in developing Euler’s column theory:

1. The column material obeys Hooke’s law

2. The failure of the column occurs due to buckling

3. The column is ‘long’ compared to its cross-sectional dimensions

Which of the above statements are correct?

(a) 1 and 2 only

(b) 1 and 3 only

(c) 2 and 3 only

(d) 1, 2 and 3

Answer: (d)

73. Plastic deformation by twinning mechanism occurs in metals due to the movement of atoms where:

1. Atoms move through distances proportional to their (original) distance from the twinning plane

2. Atoms move in integral steps of full atomic distances from their adjacent planes

3. Atoms jumps from one plane to another

Which of the above statements is/are correct?

(a) 1 only

(b) 2 only

(c) 3 only

(d) 1, 2 and 3

Answer: (a)

74. The volume of atoms in a simple cubical structure unit cell divided by the volume of the unit cell is called

(a) Volume ratio of the unit cell

(b) Volume density of the unit cell

(c) Atomic packing factor

(d) Planar density

Answer: (c)

75. Which of the following are zero dimensional defects?

1. Vacancy

2. Interstitial defect

3. Substitutional defect

(a) 1 and 2 only

(b) 1 and 3 only

(c) 2 and 3 only

(d) 1, 2 and 3

Answer: (d)

76. Which of the following is/are the characteristic features of eutectic alloys?

1. They possess the lowest melting temperature

2. They undergo phase transformation at the same temperature while heating as well as cooling

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2

Answer: (c)

77. If plain carbon steel in the austenitic condition is quenched in water to room temperature, its structure changes from ‘austenite’ to

(a) Pearlite

(b) Martensite

(c) Cementite

(d) Ferrite

Answer: (b)

78. Consider the following statements:

1. Ferrite is the softest constituent’s phase of steel

2. Pearlite is the mixture of Bainite and Ledeburite

Which of the above statements is/are correct?

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2

Answer: (a)

79. Brittle fracture takes place without any appreciable deformation and by rapid crack propagation. The direction of crack propagation is very nearly:

1. Perpendicular to the direction of the applied tensile stress

2. Parallel to the direction of the applied tensile stress

3. At an angle 45° to the direction of the applied tensile stress

Which of the above statements is/are correct?

(a) 1 only

(b) 2 only

(c) 3 only

(d) 1, 2 and 3

Answer: (a)

80. Which one of the following heat treatment process improves machinability?

(a) Annealing

(b) Process annealing

(c) Normalizing

(d) Spheroidizing

Answer: (d)

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