Tuesday, 12 February 2019

ISRO RAC 2018 Question paper with Answers


41. For a glass plate, transitivity and reflectivity are specified as 0.86 and 0.08 respectively, the absorptivity of the glass plate is
(a) 0.86                                                                                       (b) 0.06
(c) 0.08                                                                                       (d) 1.00

Answer: (b)

42. A composite slab has two layers of different materials with thermal conductivities k1 and k2 . If each layer has same thickness, then the equivalent thermal conductivity will be:
(a) $k_1 k_2$                                                                    (b) $k_1 + k_2$ 

(c) $\frac{2k_1 k_2}{(k_1 + k_2)}$                                (d)  $\frac{(k_1 + k_2)}{k_1 k_2}$

Answer: (c)

43. The ratio of heat flow Q1/Q2 from two walls of same thickness having their thermal
conductivities as K1 = 2K2 will be:
(a) 1                                                                  (b) 1/2
(c) 3/4                                                               (d) 2

Answer: (d)

44. In case of saddle key, power is transmitted by means of
(a) Friction force
(b) Shear resistance of key
(c) Torsional resistance of key
(d) Tensile force

Answer: (c)

45. The angle of twist for a transmission shaft is inversely proportional to
(a) Shaft diameter
(b) (shaft diameter)^2
(c) (shaft diameter)^3
(d) (shaft diameter)^4

Answer: (d)

46. Two mating spur gears have 40 and 120 teeth respectively. The pinion transmits at 1200 rpm and transmits a torque of 20 N-m. The torque transmitted by gear is:
(a) 60 N-m                                                                  (b) 6.6 N-m
(c) 40 N-m                                                                  (d) 66 N-m

Answer: (a)

47. The expected life of a ball bearing subjected to a load of 9800 N and operating at 1000 RPM is 3000 hrs. What is the expected life of the same bearing for similar load of 4900 N and speed of 2000 RPM
(a) 12000 hrs.                                                                  (b) Remain same
(c) 6000 hrs.                                                                  (d) 1500 hrs.

Answer: (a)

48. Neutral axis of a beam is;
(a) Layer subjected to tensile stress
(b) Layer subjected to compressive stress
(c) Layer subjected to torsion stress
(d) Layer subjected to zero stress

Answer: (d)

49. A Gas engine has a swept volume of 300 cm3 and its volumetric efficiency is 0.88 and mechanical efficiency is 0.90. The volume of mixture taken in per stroke is
(a) 248 3 cm                                                                  (b) 252 3 cm
(c) 264 3 cm                                                                  (d) 286 3 cm

Answer: (c)

50. The ratio of the brake power to indicated power is called
(a) Overall efficiency
(b) Thermal efficiency
(c) Mechanical efficiency
(d) Volumetric efficiency

Answer: (c)

51. A heat engine is supplied with 250 kJ/s of heat at a constant fixed temperature of 227°C. The heat is rejected at 27°C. If the cycle is reversible, the amount of heat rejected is :
(a) 150 kJ/s                                                                   (b) 200 kJ/s
(c) 273 kJ/s                                                                   (d) 185 kJ/s

Answer: (a)

52. A heat Engine gives an output of 3 kW when the input is 10000 joules/sec. The thermal
efficiency of the engine is
(a) 30%                                                                 (b) 20%
(c) 40%                                                                 (d) 76.7%

Answer: (a)

53. A base load power station of capacity 35 MW has annual output of 150 ×106 kWh. The plant capacity factor of the power plant is
(a) 68%                                                                 (b) 35%
(c) 49%                                                                 (d) 25%

Answer: (c)

54. Diesel engine having brake thermal efficiency of 30% and the calorific value of fuel used is
10000 kcal/kg, the brake specific fuel consumption will be
(a) 0.21 kg/HP.hr
(b) 0.29 kg/HP.hr
(c) 0.39 kg/HP.hr
(d) 0.49 kg/HP.hr

Answer: (a)

55. The control rods in the control system of nuclear reactors are used to
(a) Control fuel consumption
(b) Absorb excess neutrons
(c) Control temperature
(d) None of the above

Answer: (b)

56. Efficiency of Carnot engine is 80%. If the cycle direction is reversed, what will be the value
of COP of reversed Carnot cycle
(a) 0.25 (b) 0.5
(c) 1.25 (d) 1.5

Answer: Excluded for evaluation

57. If the evaporator temperature of a refrigeration plant is lowered, keeping condensing temperature constant, the horse power requirement of compressor will
(a) Remain same
(b) Increase
(c) Decrease
(d) More or less depending on capacity

Answer: (b)

58. For Ammonia refrigeration system, the pipe for carrying refrigerant shall be made of following material:
(a) brass                                                                  (b) copper
(c) steel or wrought iron                                          (d) aluminium

Answer: (c)

59. In psychrometric chart, relative humidity lines are:
(a) curved                                                                  (b) horizontal
(c) straight inclined from left to right                         (d) vertical

Answer: (a)

60. The operating temperature of a cold storage is –9°C and load for the refrigeration plant is
20 kW for ambient temperature of 24°C. The actual COP of the plant used is one fourth that
of ideal plant working between the same temperatures. The power required to drive the plant is:
(a) 2.5 kW                                                                  (b) 5 kW
(c) 10 kW                                                                   (d) 3 kW

Answer: (c)

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