# BSNL mechanical engineering questions for all examinsions

B**SNL mechanical engineering questions for all examinsions,BSNL JTO DGM znd other exams in 2013 model questions for practice**

1. An Aeroplane travels at 400 km/hr at sea level where the temperature is 15^{o}C. The velocity of the Aeroplane at the same Mach number at an altitude where a temperature of -25Cis prevailing, would be

a) 126.78 km/hr

b) 130.6 km/hr

c) 371.2 km/hr

d) 400.10 km/hr ** (Ans)**

2. The plot for the pressure ratio along the length of the convergent-divergent nozzle is shown in the given figure. The sequence of the flow conditions labelled 1,2,3, and 4 in the figure is respectively

a) supersonic, sonic, subsonic and supersonic

b) sonic, supersonic, subsonic and supersonic

c) subsonic, supersonic, sonic and subsonic

d) subsonic, sonic, supersonic and subsonic ** (Ans)**

3. If the full -scale turbine is required to work under a head of 30 m and to run at 428 r.p.m., then a quarter-scale turbine model tested under a head of 10 m must run at

a) 143 r.p.m.

b) 341 r.p.m.

c) 428 r.p.m.

d) 988 r.p.m.** (Ans)**

4. The dimensionless group formed by wavelength λ, density of fluid ρ, acceleration due to gravity g and surface tension σ, is

a) σ ** (Ans)**

λ^{2}gρ

b) σ

λg^{2}ρ

c) σg

λ^{2}ρ

d) ρ

λ^{2}gρ

5. Which one of the following sets of standard flows is uperimposed to represent the flow around a rotating cylinder ?

a) Doublet, vortex and uniform flow ** (Ans)**

b) Source, vortex and uniform flow

c) Sink, vortex and uniform flow

d) Vortex and uniform flow

6.

A float of cubical shape has sides of 10 cm. The float valve just touches the valve seat to have a flow area of 0.5 cm2 as shown in the given figure. If the pressure of water in the pipeline is 1 bar, the rise of water level h in the tank to just stop the water flow will be

a) 7.5 cm

b) 5.0 cm** (Ans)**

c) 2.5 cm

d) 0.5 cm

7. A U-tube manometer is connected to a pipeline conveying water as shown in the given figure. The pressure head of water in the pipeline is

a) 7.12 m

b) 6.56 m

c) 6.0 m** (Ans)**

d) 5.12

8. The eye of a tornado has a radium of 40 m. If the maximum wind velocity is 50 m/s, the velocity at a distance of 80 m radius is

a) 100 m/s

b) 2500 m/s

c) 31.25 m/s

d) 25 m/s** (Ans)**

9. If a vessel containing liquid moves downward with constant acceleration δ, then

a) the pressure throughout the liquid mass is atmosphere

b) the pressure in the liquid mass is greater than the hydrostatic pressure

c) there will be vacuum in the liquid

d) the pressure throughout the liquid mass is greater than atmosphere ** (Ans)**

10. Improve streamlining produces 25% reduction in the drag coefficient of a torpedo. When it is travelling fully submerged and assuming the driving power to remain the same, the increase in speed will be

a) 10 %** (Ans)**

b) 20 %

c) 25 %

d) 30 %

11. If a bullet is fired in standard air at 15^{o}C at the Mach angle of 30^{o}C, the velocity of the bullets would be

a) 513.5 m/s

b) 585.5 m/s

c) 645.5 m/s

d) 680.5 m/s** (Ans)**

12. A stream function is given by (x^{2}-y^{2}). The potential function of the flow will be

a) 2xy + f(x)

b) 2xy + constant** (Ans)**

c) 2(x^{2}-y^{2})

d) 2xy + f(y)

13. The height of a cylindrical container is twice that of its diameter. The ratio of the horizontal forces on the wall of the cylinder when it is completely filled to that when it is half filled with the same liquid is

a) 2** (Ans)**

b) 3

c) 3.5

d) 4

14. The velocities and corresponding flow areas of the branches labelled 1,2,3,4 and 5 for a pipe system shown in the given figure are given in the following table :

Pipe Label l |
Velocity |
Area |

1 | 5 cm/s | 4 sq cm |

2 | 6 cm/s | 5 sq cm |

3 | V_{3} cm/s |
2 sq cm |

4 | 4 cm/s | 10 sq cm |

5 | V_{5} cm/s |
8 sq cm |

a) 2.5 cm/s

b) 5 cm/s** (Ans)**

c) 7.5 cm/s

d) 10 cm/s

15. A pipe is connected in series to another pipe diameter is twice and length is 32 times that of the first pipe. The ratio of frictional head losses for the first pipe to those for the second pipe is (both the pipes have the same frictional constant)

a) 8

b) 4

c) 2

d) 1** (Ans)**

16. Which one of the following statements is correct ?

a) Hydraulic grade line and energy grade line are the same in fluid flow problems

b) Energy grade line lies above the hydraulic grade line and is always parallel to it

c) Energy grade line lies above the hydraulic grade line and they are separated from each other by a vertical distance equal to the velocity head ** (Ans)**

d) The hydraulic grade line slopes upwards meeting the energy grade line only at the exit of flow

17. If laminar flow takes place in two pipes, having relative roughnesses of 0.002 and 0.003, at a Reynolds number of 1815, then

a) the pipe of relative roughness of 0.003 has a higher friction factor ** (Ans)**

b) the pipe of relative roughness of 0.003 has a lower friction factor

c) both pipes have the same friction factor

d) no comparison is possible due to inadequate data

18. A pipeline connecting two reservoirs has its diameter reduced by 20% due to deposition of Chemicals. For a given head difference in the reservoirs with unaltered friction factor, this would cause a reduction in discharge of

a) 42.8% ** (Ans)**

b) 20%

c) 17.8%

d) 10.6%

19. A tank containing water has two orifices of the same size at depths of 40 cm and 90 cm below the free surface of water. The ratio of discharges through these orifices is

a) 1:1

b) 2:3 ** (Ans)**

c) 4:9

d) 16:81

20. A Pilot static tube is used to measure the velocity of water using a differential gauge which contains a manometric fluid of relative density 1.4. The deflection of the gauge fluid when water flows at a velocity of 1.2 m/s will be (the coefficient of the tube may be assumed to be 1)

a) 183.5 mm

b) 52.4 mm ** (Ans)**

c) 5.24 mm

d) 73.4 mm

21. The development of boundary layer zones labelled P,Q, R and S over a flat plate is shown in the given figure

Based on this figure, match List (Boundary layer zones) with List II (Types of boundary layer) and select the correct answer using the codes given below the Lists :

List -I List -II

a) P 1. Transitional

b) Q 2. Laminar viscous sub-layer

c) R 3. Laminar

d) S 4. Turbulent

Codes :

A B C D

a) 3 1 2 4** (Ans)**

b) 3 2 1 4

c) 4 2 1 3

d) 4 1 2 3

22. A pipe of 20 cm diameter and 30 km length transports oil from a tanker to the shore with a velocity of 0.318 m/s. The flow is laminar. If μ = 0.1 N-m/s^{2}, the power required for the flow would be

a) 9.25 kW** (Ans)**

b) 8.36 kW

c) 7.63 kW

d) 10.13 kW

23. In a turbulent boundary layer over the entire length of a plate, the boundary layer thickness increases with its distance X from the leading edge as

a) X ^{1/2}

b) X^{1/5}

c) X^{2/5}

d) X^{4/5}** (Ans)**

24. Separation of fluid flow is caused by

a) reduction of pressure in the direction of flow

b) reduction of the boundary layer thickness

c) presence of adverse pressure gradient** (Ans)**

d) presence of favourable pressure gradient

e) presence of adverse pressure gradient

25. When pressure drag over a body is large as compared to the friction drag, then the shape of the body is that of

a) an aerofoil

b) a streamlined body

c) a two-dimensional body

d) a bluff body** (Ans)**

26. A circular cylinder of 400 mm diameter is rotated about its axis in a stream of water having a uniform velocity of 4 m/s. When both the stagnation points coincide, the lift force experienced by the cylinder is

a) 160 kN/m

b) 10.05 kN/m** (Ans)**

c) 80 kN/m

d) 40.2 kN/m

27. An automobile moving at a velocity of 40km/hr is experiencing a wind resistance of 2kN. If the automobile is moving at a velocity of 50km/hr, the power required to overcome the wind resistance is

a) 43.4kW** (Ans)**

b) 3.125 kW

c) 2.5 kW

d) 27.776 kW

28. When a cylinder is placed in an ideal fluid and the flow is uniform, the pressure coefficient Cp is equal to

a) 1-sin^{2}θ ** (Ans)**

b) 1- 2 sin^{2}θ

c) 1- 4 sin^{2}θ

d) 1- 8 sin^{2}θ

29. If the upstream Mach number of a normal shock occuring in air (k=1.4) is 1.68, then the Mach number after the shock is

a) 0.84

b) 0.646** (Ans)**

c) 0.336

d) 0.564

30. Which one of the following sets of thermodynamic laws/ relations is directly involved in determining the final properties during an adiabatic mixing process?

a) The first and second laws of thermodynamics

b) The second law of thermodynamics and steady flow relations

c) Perfect gas relationship and steady flow relations

d) The first law of thermodynamics and perfect gas relationship ** (Ans)**

31. The air wiht enthalpy of 100 kJ/kg is compressed by an air compressor to a pressure and temperature at which its enthalpy becomes 200 kJ/kg. The loss of heat is 40kJ/kg from the compressor as the air passes through it. Neglecting kinetic and potential energies, the power required for an air mass flow of 0.5 kg/s is

a) 30kW** (Ans)**

b) 50kW

c) 70kW

d) 90kW

32. Consider the following statements :

i) The first law of thermodynamics is a law of conservation of energy

ii) Perpetual motion machine of the first kind converts energy into euivalent work

iii) A closed system does not exchange work or energy with its surroundings

iv) The second law of thermodynamic stipulates the law of conservation of energy and entropy. Which of the statements are correct ?

a) (i) and (iii)

b) (ii) and (iv)

c) (ii), (iii) and (iv)

d) (i), (ii) and (iii) ** (Ans)**

33. A heat engine receives 1000 kW of heat at a constant temperature of 285 ^{ o}C and rejects 492 kW of heat at 5^{o}C. Consider the following thermodynamic cycles in this regard:

(i) Carnot cycle

(ii) Reversible cycle

(iii) Irreversible cycle

Which of these cycles could possible be executed by the engine ?

a) 1 alone ** (Ans)**

b) 3 alone

c) 1 and 2

d) None 1, 2 and 3

34. The process 1-2 for steam shown in the given figure is

a) isobaric

b) isentropic

c) isenthalpic** (Ans)**

d) isothermal

35. In which one of the following working substances, does the relation T2 = (P2)^{0.286} hold good if the process takes place with zero heat transfer ?

T1 P1

a) West steam

b) Superheated steam ** (Ans)**

c) Petrol vapour and air mixture

d) Air

36. Consider the following statements :

When dry saturated steam is throttled from a higher pressure to a lower pressure, the

a) pressure decreases and the volume increases ** (Ans)**

b) temperature decreases and the steam becomes superheated

c) temperature and the dryness fraction increase

d) entropy increases without any change in enthalpy

37. In which one of the following situations the entropy change will be negative

a) Air expands istothermally from 6 bars to 3 bars ** (Ans)**

b) Air is compressed to half the volume at constant pressure

c) Hear is supplied to air at constant volume till the pressure becomes three folds

d) air expands isentropically from 6 bars to 3 bars

38. The heat added to a closed system during a reversible process is given by Q = αT + βT^{2}, where α and β are constants. The entropy change of the system as its temperature changes from T_{1} to T_{2} is equal to

39. The internal energy of a gas obeying van der Waals equation (p + a/V_{2}) (v-b) = RT depends on its

a) temperature

b) temperature and pressure ** (Ans)**

c) temperature and specific volume

d) pressure and specific volume

40. Consider the following statements :

A real gas obeys perfect gas law at very

(i) high temperature

(ii) high pressure

(iii) low pressures

Which of these statements is/are correct ?

a) (i) alone

b) (i) and (iii)

c) (ii) alone

d) (iii) alone ** (Ans)**

41. The capacity of an air compressor is specified as 10 m^{3}/min. It means that the compressor is capable of

a) supplying 3 m^{3} of compressed air per minute ** (Ans)**

b) compressing 3 m^{3} of free air per minute

c) supplying 3 m^{3} of compressed air at NTP

d) compressing 3 m^{3} of standard air per minute

42. A two-stage compressor takes in air at 1.1 bars and discharges at 20 bars. For maximum efficiency, the intermediate pressure is

a) 10.55 bars

b) 7.33 bars

c) 5.5 bars

d) 4.7 bars ** (Ans)**

43. For the same maximum pressure and heat input, the most efficient cycle is

a) Otto cycle ** (Ans)**

b) Diesel cycle

c) Brayton cycle

d) Dual combustion cycle

44. In a petrol engine car, which one of the following performance characteristics is affected by the front-end volatility of the gasoline used ?

a) Hot starting and vapour lock

b) Engine warm -up and spark plug fouling

c) Spark plug fouling and hot starting

d) Vapour lock, engine warm -up and spark plug fouling ** (Ans)**

45. In turbo prop, the expansion of gases takes place approximately

a) 100% in the turbine ** (Ans)**

b) 80% in the turbine and 20% in the nozzle

c) 50% in the turbine and 50% in the nozzle

d) 100% in the nozzle

46. The most commonly used moderator in Nuclear power plants is

a) heavy water

b) concrete and bricks

c) steel

d) graphite ** (Ans)**

47. Shielding in a nuclear reactor is generally done to protect against

a) excess electrons

b) X-rays

c) α and β rays

d) neutron and gamma rays ** (Ans)**

48. Partial admission steam turbine refers to the situation where the

a) steam is admitted partially into the blades through nozzles ** (Ans)**

b) nozzles occupy the completer circumference leading into the blade annulum

c) nozzles do not occupy the complete circumference leading into the annulus

d) steam is admitted partially into the blades directly.

49. In a steam power plant, the ratio of the isentropic heat drop in the prime mover to the amount of heat supplied per unit mass of steam is known as

a) stage efficiency

b) degree of reaction

c) Rankine efficiency ** (Ans)**

d) relative efficiency

50. Reciprocating compressors are provided with

a) simple disc/plate valve ** (Ans)**

b) poppet valve

c) spring-loaded disc valve

d) solenoid valve

51. The gross head available to hydraulic power plant is 100m. The utilised head in the runner of the hydraulic turbine is 72 m. If the hydraulic efficiency of the turbine is 90% , the pipe friction head is estimated to be

a) 20 m ** (Ans)**

b) 18 m

c) 16.2 m

d) 1.8 m

52. Which one of the following pairs of formulae represents the specific speeds of turbine and pump respectively ? (Notations have their usual meanings)

a) NQ ^{1/2} and NP^{1/2}

H^{3/4} H^{5/4 }

b) NQ ^{1/2} and NP^{1/2}

H^{3/4} H^{3/4}

c) NP^{1/2} and NQ^{1/2}

H^{3/4} H^{5/4 }

d) NP ^{1/2} and NQ^{1/2} ** (Ans)**

H^{5/4 } H^{3/4}

53. The outer surface of a long cylinder is maintained at constant temperature. The cylinder does not have any heat source

The temperature in the cylinder will

a) increase linearly with radius

b) decrease linearly with radius

c) be independent of radius ** (Ans)**

d) vary logarithmically with radius

54. A composite plane wall is made up of two different materials of the same thickness and having a thermal conductivities of k1 and k2 respectively. The equivalent thermal conductivity of the slab is

a) k1+k2

b) k1k2

c) k1+k2** (Ans)**

k1k2

d) 2k1k2

k1+k2

55. A copper wire of radius 0.5 mm is insulated with a sheathing of thickness 1 mm having a thermal conductivity of 0.5 W/m-K. The outside convective heat transfer coefficient is 10W/m^{2}-K. If the thickness of insulation sheathing is raised by 10 mm, then the electrical current-carrying capacity of the wire will

a) increase

b) decrease

c) remain the same** (Ans)**

d) vary depending upon the electrical conductivity of the wire

56. For the fully developed laminar flow and heat transfer in a uniformly heated long circular tube, if the flow velocity is doubled and the tube diameter is halved, the heat transfer coefficient will be

a) double of the original value

b) half of the original value** (Ans)**

c) same as before

d) four times of the original value

57. Heat transfer by radiation between two grey bodies of emissivity ε is proportional to (notations have their usual meanings)

a) (E_{b} – J)

(I – ε)

b) (E_{b} – J)** (Ans)**

(I – ε) /ε

c) (E_{b} – J)

(I – ε)^{2}

d) (E_{b} – J)

(I – ε^{2})

58. The Nusselt number is related to Reynolds number in laminar and turbulent flows respectively as

a) Re^{-1/2} and Re^{0.8 }

b) Re^{1/2 }and Re^{0.8}** (Ans)**

c) Re^{-1/2} and Re^{-0.8}

d) Re1/2 and Re^{-0.8 }

59. In respect of free convection over a vertical flat plate the Nusselt number varies with Grashof number ‘Gr’ as

a) Gr and Gr^{1/2} for laminar and turbulent flows respectively ** (Ans)**

b) Gr^{ 1/2} and Gr^{1/3} for laminar and turbulent flows respectively

c) Gr^{1/4} and Gr^{1/3 }for laminar and turbulent flows respectively

d) Gr^{1/3} and Gr^{1/4} for laminar and turbulent flows respectively

60. The enthalpies at the beginning of compression, at the end of compression and at the end of condensation are respectively 185 kJ/kg and 85 kJ/kg. The COP of the vapour compression refrigeration system is

a) 0.25

b) 5.4

c) 4 ** (Ans)**

d) 1.35

61. The COP of a heat pump β_{HP }and the COP of a refrigerator β_{Ref} are related as

a) β_{HP + }β_{Ref}

b) β_{HP – }β_{Ref }= 1** (Ans)**

c) β_{Ref – }β_{HP} = 1

d) β_{HP – }β_{Ref }= 0

62. The discharge pressure of the compressor in the refrigeration system goes up due to the

a) lower volumetric efficiency of the compressor

b) formation of scale in the condenser** (Ans)**

c) large size of the condenser

d) undercharge of the refrigerant

63. The leakage in a Freon-based refrigeration system can be detected by using a/an

a) oxy-acetylene torch

b) halide torch** (Ans)**

c) sulphur torch

d) blue litmus paper

64. When warm saturated air is cooled

a) excess moisture condenses** (Ans)**

b) excess moisture condenses but relative humidity remains unchanged

c) excess moisture condenses and specific humidity increases but relative humidity remains unchanged.

d) specific humidity increases and relative humidity decreases

65. When dry-bulb and wet-bulb temperature are identical, it means that the

a) air is fully saturated and dew-point temperature has reached

b) air is fully saturated ** (Ans)**

c) dew-point temperature has reached and humidity is 100%

d) partial pressure of water vapour is equal to total pressure

66. The desirable air velocity in the occupied zone for comfort for summer air-conditioners is in the range of

a) 6-7 m/minute

b) 4-5m/minute

c) 2-3 m/minute

d) 0.5-1.5 m/minute ** (Ans)**

67. An air-conditioned room of volume 10 cm3 has infiltration of air equivalent to 3 air changes. Density of air is 1.2 kg/3, specific heat Cp is 1 kJ/kg-K and temperature difference between room and ambient air is 20K. The sensible heat load due to infiltrated air is

a) 60 kJ/hr

b) 12 kJ/hr

c) 6 kW

d) 0.2 k W ** (Ans)**

68. If heat and mass transfer take place simultaneously, the ratio of heat transfer coefficient to the mass transfer coefficient is a function of the ratio of

a) Schmidt and Reynolds numbers ** (Ans)**

b) Schmidit and Prandtl numbers

c) Nusselt and Lewis number

d) Reynolds and Lewis numbers

69. Consider the following statements :

The typical air velocities in the ducts of air-conditioning systems are

(i) lower in residential buildings as compared to those of public buildings

(ii) higher in residential buildings as compared to those of public buildings

(iii) higher in industrial buildings as compared to those of public buildings

(iv) equal in all types of buildings

Which of these statements is/are correct ?

a) (i) alone

b) (i) and (iii) ** (Ans)**

c) (ii) and (iii)

d) (iv) alone

70. Consider the following parameters :

(i) Dry-bulb temperature

(ii) Humidity ratio

(iii) Air velocity

(iv) Solar radiation intensity

Which of these parameters are taken into account for determining effective temperature for human comfort ?

a) (i) and (ii)

b) (i) and (iv)

c) (ii), (iii) and (iv)

d) (i), (ii) and (iii) ** (Ans)**