Monday, 11 February 2019

ISRO RAC 2018 Question paper with Answers



21. The purpose of thermostat in an engine cooling system is to
(a) Indicate coolant temperature
(b) Prevent coolant from boiling
(c) Allow the engine to warm up quickly
(d) Pressurize coolant for effective cooling

Answer: (c)

22. In a boiler, feed water supplied per hour is 205 kg while coal fired per hour is 23 kg. The net
enthalpy rise per kg of water is 145 kj. If the calorific value of coal is 2050 kj/kg, then boiler
efficiency will be
(a) 56%                                                                                           (b) 75%
(c) 48%                                                                                           (d) 63%

Answer: (d)

23. A throttle governed steam engine develops 15 kW with 280 kg power of steam and 35 kW
with 520 kg per hour of steam. The steam consumption in kg per hour when developing
20 kW of power will be nearly
(a) 340 kg/hr                                                                                           (b) 150 kg/hr
(c) cannot be calculated                                                                          (d) 280 kg/hr

Answer: Excluded for evaluation

24. A fluid which obeys Newton’s law of viscosity is termed as
(a) Real fluid                                                                                           (b) Newtonian fluid
(c) Non-Newtonian fluid                                                                         (d) Ideal fluid

Answer: (b)

25. A water tank contains 1.3 m deep water. The pressure exerted by water per metre length of
tank is
(a) 8.29 kN                                                                                           (b) 18.29 kN
(c) 28.9 kN                                                                                           (d) 0.28 kN

Answer: Excluded for evaluation

26. The gauge pressure at the surface of a liquid of density 900 kg/m3 is 0.4 bar. If the
atmospheric pressure is 1×105 pa, the absolute pressure at a depth of 50 M is
(a) 5.81 bar                                                                                           (b) 15.8 bar
(c) 25.8 bar                                                                                           (d) 0.5 bar

Answer: (a)

27. In Hydro-Electric plants, power transmitted through pipe is maximum when the head lost
due to friction is
(a) One fourth of the total supply head
(b) One half of the total supply head
(c) One third of the total supply head
(d) Two third of the total supply head

Answer: (c)

28. Reynolds number is ratio of Inertial forces to
(a) Elastic force                                                                                           (b) Surface tension
(c) Critical velocity                                                                                      (d) Viscous force

Answer: (d)

29. A pelton wheel develops 1750 kW under a head of 100 mts while running at 200 rpm and
discharging 2500 litres of water per sec. The unit power of wheel will be
(a) 3.75 kW                                                                                           (b) 0.75 kW
(c) 1.75 kW                                                                                           (d) 0.25 kW

Answer: (c)

30. Power required to drive a centrifugal pump is
(a) Directly proportional to speed of its impeller
(b) Directly proportional to square of the speed of its impeller
(c) Directly proportional to cube of the speed of its impeller
(d) Inversely proportional to cube of the speed of its impeller

Answer: (c)

31. The specific speed of a centrifugal pump delivering 810 Litres of water per sec. against head
of 16 mts. at 725 RPM is
(a) 81 RPM                                                                                           (b) 810 RPM
(c) 40 RPM                                                                                           (d) 16 RPM

Answer: Excluded for evaluation

32. A centrifugal pump delivers 1000 lts per minute at 2000 RPM against total head of 50 mts.
and requires 32 BHP for its operation. If speed is reduced to 1000 RPM, the discharge and
head developed will be
(a) 500 lts/min and 25 Mtr
(b) 500 lts/min and 12.5 Mtr
(c) 250 lts/min and 12.5 mtr
(d) 250 lts/min and 25 mtr

Answer: (b)

33. A flow is said to be supersonic, if the
(a) If the velocity of flow is very high
(b) Mach number is between 1 and 6
(c) Mach number is more than 6
(d) If the discharge is difficult to measure

Answer: (b)

34. Fouling factor is used in heat exchangers due to
(a) Factor in case of Newtonian fluids
(b) Safety factor in design
(c) Due to fluid leakage
(d) When liquid exchanges heat with vapour

Answer: (b)

35. In a Counter flow heat exchanger design, fluid rates and specific heats were chosen in such
a manner that heat capacities of both the fluids are same. A hot fluid enters at 100°C and
leaves at 60°C. The cold fluid enters heat exchanger at 40 °C. The mean temperature
difference between the two fluids is
(a) 40°C                                                                                           (b) 60°C
(c) 20°C                                                                                           (d) 36.6°C

Answer: (b)

36. The unit of overall coefficient of heat transfer is:
(a) W/m2°K.                                                                                           (b) W/m2
(c) W/m°K.                                                                                           (d) W/m

Answer: (a)

37. The heat transfer by conduction through a thick cylinder of inner radius 1 r , outer radius 2 r ,
Higher temperature 1 T , lower temperature 2 T , length of cylinder l and thermal conductivity
k is given by:
(a)  \(\frac{2 \pi L K(T_1 -T_2)}{2.3 log(r_2/r_1)}\)

(b) \(\frac{2.3 log(r_2/r_1)}{2 \pi L K(T_1 -T_2)}\)

(c) \(\frac{2 \pi (T_1 -T_2)}{2.3 LKlog(r_2/r_1)}\)

(d)\(\frac{2 \pi L K}{2.3(T_1 -T_2) log(r_2/r_1)}\)

Answer: (a)

38. According to Stefan-Boltzmann law, the total radiation from black body per second per unit
area is directly proportional to the
(a) Absolute temperature
(b) Fourth power of absolute temperature
(c) Cube of the absolute temperature
(d) Square of the absolute temperature

Answer: (b)

39. In a condenser of a power plant, the steam condenses at temperature of 60°C. The cooling
water enters at 30°C and leaves at 45°C. The logarithmic mean temperature difference will
be around
(a) 20°C                                                                                           (b) 80°C
(c) 200°C                                                                                         (d) 5°C

Answer: (a)

40. In shell and tube heat exchanger, baffles are mainly used for
(a) Increase the mixing of fluid
(b) Direct the flow in desired direction
(c) Reduce fouling of the tube surface
(d) Increase the heat transfer area

Answer: Excluded for evaluation


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