71. Punching shear strength of a dry rock specimen is reckoned to be nearly:

(a) Equal to the value of a wet rock specimen

(b) Twice the value of a wet rock specimen

(c) Thrice the value of a wet rock specimen

(d) Less than the value of a wet rock specimen

Answer: (c)

72. Shear strength of rock is influenced by:

(a) Cohesion

(b) Dilatancy

(c) Internal friction

(d) Cohesion, dilatancy and internal friction

Answer: (d)

73. Which one of the following statements is correct?

(a) The harder and more coherent the strata, the greater the angle of draw, and steeper the line of fracture

(b) The softer the strata, the greater the angle of draw, and flatter the line of fracture

(c) The softer the strata, the smaller the angle of draw, and flatter the line of fracture

(d) The harder and more coherent the strata, the greater the angle of draw, and flatter the line of fracture

Answer: (b)

74. Which one of the following type of crushers is normally selected for crushing tough, hard and abrasive materials?

(a) Double toggle Blake

(b) Double toggle Blake

(c) Dodge

(d) Jaw

Answer: (a & b)

75. Compressive strength of a rock:

(a) Decreases with an increase in its porosity

(b) Increases with an increase in its porosity

(c) Decreases with a decrease in its porosity

(d) Remains constant with minor changes in its porosity

Answer: (a)

76. In case of roll crushers, the relationship between co-efficient of friction 𝜇 offered by roll and the angle of nip 𝜃 is:

Answer: (a)

77. What is the speed required to perform the operation of drilling a hole of 20 mm diameter at a cutting speed of 25 m/min?

(a) 398 rpm

(b) 492 rpm

(c) 548 rpm

(d) 624 rpm

Answer: (a)

78. Crushers used in handling friable, sticky, frozen and less abrasive feeds are:

(a) Jaw crushers

(b) Gyratory crushers

(c) Roll crushers

(d) Either jaw, or roll, crushers

Answer: (c)

79. A hole of 25 mm diameter and 62.5 mm depth is to be drilled, the suggested feed is 1.25 mm/rev and the cutting speed is 60 m/min . If the tool approach and tool over travel is 5 mm , the cutting time will be nearly:

(a) 0.10 min

(b) 0.09 min

(c) 0.08 min

(d) 0.07 min

Answer: (d)

80. A hole is being drilled in a block of magnesium alloy with a 10 mm drill at a feed of 0.25 mm/rev. When the spindle is running at 1000 rpm , the material removal rate will be nearly:

Answer: (b)