Mechanical Engineering IAS Pre Exam Questions And Answers

Q. What is the fundamental unit of enthalpy?

ML²T^-2

Q. If integration pdv and -pdv for a thermodynamic system of an ideal gas on evaluation give the same quantity during a process, then the process undergone by the system is...

Isothermal

Q. In a steam condenser the partial pressure of steam and air are 0.06 bar and 0.007 bar respectively the condenser pressure is...

0.067 bar

Q. Which law of thermodynamics will be violated, if the thermal efficiency of an engine becomes 100%

Second Law

Q. The change in enthalpy of a closed system is equal to the heat transferred, if the reversible process takes place at constant?

Pressure

Q. The COP of a Carnot refrigeration cycle decreases on what?

Ans. Increasing the upper temp. and decreasing the lower temp.

Q. The correct sequence of vapour compression(VC) Vapour Absorption(VA) and Steam Injection(SE) refrigeration cycles in increasing order of the COP is....

Ans. VA, SE, VC

Q. Flash chamber is used in refrigeration for which one of following?

Ans. Effective inter cooling medium for purpose of increasing COP

Q. The significant advantage of using Ammonia as a refrigerant is its

Ans High Latent Heat

Q. Which refrigerant mostly used in mostly all domestic and car air-conditioners now a days

Ans. R-134a

Q. The color of the flame of halide torch,in a case of leakage of Freon refrigerant,will change to...

Ans. Orange

Q. Which refrigerant has the highest critical temperature?

Ans. Water

Q. In on-off control refrigeration system, which one of the following expansion device is used?

Ans. Thermostat

Q. Which is the main process which takes place in a desert-cooler?

Ans.Adiabatic Saturation

Q. If the measured wet-bulb temperature and the thermodynamic wet-bulb temp.are equal, then the non dimensional number with a value of unity is...

Ans. The Lewis Number

Q. In an ideal vapour compression refrigeration cycle, the enthalpy of the refrigerant before and after the evaporator are respectively 75 KJ/KG and 180 KJ/KG. The circulation rate of the refrigerant for each of refrigeration is....?

Ans. 2 kg/min

Q. When the mixture of refrigerant is used to replace a refrigerant , if the cop increase, the attributed is..

Ans. Increase in cooling effect

Q. Which of the following thermodynamic process is adopted in the process of summer air-conditioning?

Ans. Cooling and de humidification

Q. Air standard diesel cycle a compression ratio 14 and cut off takes place at 6% of the stroke. What is the cut off ratio?

Ans. 1.78

Q. Consider the following:

1 Increased Cetane Number

2 Increased compression ratio

3 Increased injection Advance

4 Increased air Turbulence

Which of the above factors reduces physical delay in the diesel engine?

Ans. 2 and 4 only

Q. Consider the following:

Diesel engine knock can be reduced by increasing

1 Engine Speed

2 Compression Ratio

3 Degree of Supercharge

4 Injection Advance

Which of the above statement is/are correct?

Ans. 2 and 3

Q. Self ignition temp. of diesel as compare to petrol is?

Ans. Lower

Q. For a four cylinder vertical engine, the commonly used firing order is...

Ans. 1-3-4-2

Q. What is the dimension of kinematic viscosity of a fluid?

Ans. L²T^-1

Q. What is the belonging category of hydraulic coupling?

Ans. Energy Transfer Machine

Q. What should be to avoid cavitation in the centrifugal pump?

Ans. Suction pressure should be high

Q. An increase in pressure of 2 bars decrease the volume of a liquid by 0.01 percent .What would be the bulk modulus of elasticity of liquid?

Ans. 2*10⁹ N/m²

Q. If a fluid jet is discharging from 50 mm diameter orifice has a 40 mm diameter at its vena contracts, then what will be its coefficient of contraction?

Ans. 0.64

Q. The pressure drop for a relatively low Reynolds number flow in a 600 mm, 30 m long pipe line is 70 kPa. What is the wall shear stress.

Ans. 350 Pa

Q. A centrifugal pump having an impeller of 10 cm diameter discharge 40 liter/second when running at 1000 rpm. What will be the corresponding speed of a geometrically similar pump having an impeller of 40 cm diameter and 0.8 m³/S discharge?

Ans. 312.5 rpm

Q. In steam generators, a stokers acts as one of the following devices. What is this device?

Ans. Fuel feeding device

Q. Which thermal power plant has the highest overall thermal efficiency?

Ans. Combine gas and steam power plant

Q. In Rankine cycle ,the heat rejection process takes place at constant?

Ans. Pressure

Q. In Rankine cycle the lower limit on condenser pressure is due to the...?

Ans. Condenser Size

Q. Reheating of steam under ideal condition takes place at constant

Ans Pressure

Q. In which process turbine steam is taken from various points along the turbine , slowely for feed water heating?

Ans. Regenerative Turbine

Q. What is the value of reheat factor in multistage turbine?

Ans 1.03 to 1.04

Q. Which of the following method is are adopted to bring down the speed of an impulse turbine to practical limits?

1 Use of flywheel

2 Use of governor

3 Compounding

4 Increasing the load

Select the correct answer..

Ans. 3 Compounding

Q. What is the prime parameter causing change of state in a Fanno Flow?

Ans. Friction

Q. Which type of nuclear reactor does not require a heat exchanger?

Ans. Boiling Water

Q. What is the energy released during the fission of one U-235 atom?

Ans. 200 Mev

Q. Cooling tower in a steam power station is a device

Ans. Reducing the temp. of cooling water used in condenser

Q. What is the difference between the feed water outlet and saturation temperature of steam entering the heater called?

Ans. Terminal temp. difference

Q. Which cycle works with in the same limits has the highest work ratio?

Ans. Rankine Cycle

Q. The percentage elongation of a material as obtain from static tension test depends upon which factor?

Ans. Gauge length of the specimen

Q. Modulus of elasticity is what kind of property?

Ans. A property to store energy without undergoing paramount deformation

Q. What causes a short steel strut fail?

Ans. Fracture

Q. A mild steel specimen is tested in tension up to fracture in a universal testing machine. Which of the following mechanical properties of the material can be evaluated from such a test?

1 Modulus of elasticity

2 Yield Stress

3 Ductility

4 Tensile Strength

5 Hardness

6 Modulus of rigidity

Select the correct answers from the given answers.

Ans. 1,2,3 and 4

Q. Consider the following statements.

1 There are only two independent elastic constants

2 Elastic constants are different in orthogonal directions

3 Material properties are same everywhere

4 Elastic constants are same in all loading directions

5 The material have the capacity to withstand the shock loading

Which of the above statements are correct for a linearly elastic,homogeneous and isotropic material?

Ans 1,3 and 4

Q. A closed coil helical spring has wire diameter 10 mm and spring index 5. If the spring contains 10 turns, then the length of the spring wire would be..?

Ans 1570 mm

Q. A Hartnell governor is a type of governor?

Ans. Centrifugal type

Q. The problem of hunting of a centrifugal governor becomes very actuate when the governer becomes?

Ans. Highly Sensitive

Q. In case of a flywheel of mass moment of inertia 'I' rotating at an angular velocity 'w' the expression 1/2 Iw² represents the...?

Ans. Kinetic Energy

Q. Whirling speed of a shaft coincides with the natural frequency of its...?

Ans. Transverse Vibration

Q. A point on a connecting link of a double slider crank mechanism traces a path?

Ans. Elliptical Path

Q. If an imaginary circle is drawn which by pure rolling actions give the same motion as the actuate gear , What is the circle called?

Ans. Pitch Circle

Q. How does the contact ratio of the helical gear compare with that of spur gear?

Ans. It is greater then that of spur gear