Thermodynamics

JKSSB Junior Engineer (Mechanical) · Technical Subjects (Mechanical) · 29 practice questions with answers and explanations: 16 Easy, 13 Medium, 0 Hard.

Sample questions

Sample Easy question 1

The dryness fraction of wet steam is:

  1. Volume of steam divided by volume of water
  2. Zero for dry saturated steam
  3. Mass of water divided by total mass
  4. Mass of dry steam divided by total mass of the mixture
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Answer: D. Dry saturated steam has a dryness fraction of 1.

Sample Easy question 2

The components of a simple Rankine cycle are:

  1. Evaporator, compressor, condenser and expansion valve
  2. Compressor, combustion chamber, turbine and heat exchanger
  3. Cylinder, piston, spark plug and crankshaft
  4. Boiler, turbine, condenser and pump
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Answer: D. The Rankine cycle is the basic steam power plant cycle.

Sample Easy question 3

The characteristic gas constant of air is about:

  1. 1.4 J/kg·K
  2. 8.314 J/kg·K
  3. 4,186 J/kg·K
  4. 287 J/kg·K
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Answer: D. R for air is about 287 J/kg·K, while 8.314 J/mol·K is the universal gas constant.

Sample Medium question 4

1 kg of air (Cv = 0.718 kJ/kg·K) is heated at constant volume from 300 K to 400 K. The heat added is about:

  1. 100.5 kJ
  2. 0.718 kJ
  3. 71.8 kJ
  4. 28.7 kJ
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Answer: C. Q = m·Cv·ΔT = 1 × 0.718 × 100 = 71.8 kJ.

Sample Medium question 5

A Carnot engine takes 1,000 kJ of heat from a source at 800 K and rejects heat at 400 K. The work done is:

  1. 250 kJ
  2. 800 kJ
  3. 500 kJ
  4. 400 kJ
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Answer: C. Efficiency = 1 − 400/800 = 0.5, so work = 0.5 × 1,000 = 500 kJ.

Sample Medium question 6

Air at 1 bar and 300 K is heated in a rigid vessel until its pressure is 4 bar. The final temperature is:

  1. 600 K
  2. 900 K
  3. 75 K
  4. 1,200 K
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Answer: D. At constant volume p/T is constant, so T2 = 300 × 4 = 1,200 K.

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