Mechanical Engineering Thermodynamics – Set 18

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Q1. The value of gas constant (R) in S. I. units is

(A) 0.287 J/kgK
(B) 2.87 J/kgK
(C) 28.7 J/kgK
(D) 287 J/kgK

Answer: (D) 287 J/kgK

Q2. The entropy __ in an irreversible cyclic process.

(A) Remains constant
(B) Decreases
(C) Increases
(D) None of these

Answer: (C) Increases

Q3. If in the equation pvn = C, the value of n = ∝, then the process is called

(A) Constant volume process
(B) Adiabatic process
(C) Constant pressure process
(D) Isothermal process

Answer: (A) Constant volume process

Q4. Charles’ law states that all perfect gases change in volume by __ of its original volume at 0°C for every 1°C change in temperature, when pressure remains constant.

(A) 1/27th
(B) 1/93th
(C) 1/173th
(D) 1/273th

Answer: (D) 1/273th

Q5. In a free expansion process,

(A) W1 – 2 = 0
(B) Q1 – 2 = 0
(C) dU = 0
(D) All of these

Answer: (D) All of these

Q6. The efficiency and work ratio of a simple gas turbine cycle are

(A) Low
(B) Very low
(C) High
(D) Very high

Answer: (B) Very low

Q7. When gas is heated at constant pressure, the heat supplied is utilized in

(A) Increasing the internal energy of gas
(B) Doing some external work
(C) Increasing the internal energy of gas and also for doing some external work
(D) None of the above

Answer: (C) Increasing the internal energy of gas and also for doing some external work

Q8. The work ratio of simple gas turbine cycle depends upon

(A) Maximum cycle temperature
(B) Minimum cycle temperature
(C) Pressure ratio
(D) All of these

Answer: (D) All of these

Q9. Stirling cycle consists of

(A) Two constant volume and two isentropic processes
(B) Two constant volume and two isothermal processes
(C) Two constant pressure and two isothermal processes
(D) One constant volume, one constant pressure and two isentropic processes

Answer: (B) Two constant volume and two isothermal processes

Q10. One Joule (J) is equal to

(A) 1 N-m
(B) 1 kN-m
(C) 10 N-m/s
(D) 10 kN-m/s

Answer: (A) 1 N-m

Q11. When a gas is heated, change takes place in

(A) Pressure
(B) Volume
(C) Temperature
(D) All of these

Answer: (D) All of these

Q12. Select the correct statement as per Charles’ law

(A) p.v = constant, if T is kept constant
(B) v/T = constant, if p is kept constant
(C) p/T = constant, if v is kept constant
(D) T/p = constant, if v is kept constant

Answer: (B) v/T = constant, if p is kept constant

Q13. The universal gas constant (or molar constant) of a gas is the product of

(A) Molecular mass of the gas and the gas constant
(B) Atomic mass of the gas and the gas constant
(C) Molecular mass of the gas and the specific heat at constant pressure
(D) Molecular mass of the gas and the specific heat at constant volume

Answer: (A) Molecular mass of the gas and the gas constant

Q14. The hyperbolic process is governed by

(A) Boyle’s law
(B) Charles’ law
(C) Gay-Lussac law
(D) Avogadro’s law

Answer: (A) Boyle’s law

Q15. The compression ratio for Diesel engines is

(A) 3 to 6
(B) 5 to 8
(C) 15 to 20
(D) 20 to 30

Answer: (C) 15 to 20

Q16. For a perfect gas, according to Boyle’s law (where p = Absolute pressure, v = Volume, and T = Absolute temperature)

(A) p v = constant, if T is kept constant
(B) v/T = constant, if p is kept constant
(C) p/T = constant, if v is kept constant
(D) T/p = constant, if v is kept constant

Answer: (A) p v = constant, if T is kept constant

Q17. The value of specific heat at constant pressure (cp) is __ that of at constant volume (cv).

(A) Less than
(B) Equal to
(C) More than
(D) None of these

Answer: (C) More than

Q18. A mixture of gas expands from 0.03 m3 to 0.06 m3 at a constant pressure of 1 MPa and absorbs 84 kJ of heat during the process. The change in internal energy of the mixture is

(A) 30 kJ
(B) 54 kJ
(C) 84 kJ
(D) 114 kJ

Answer: (B) 54 kJ

Q19. When the gas is heated at constant volume, the heat supplied

(A) Increases the internal energy of the gas and increases the temperature of the gas
(B) Does some external work during expansion
(C) Both (A) and (B)
(D) None of these

Answer: (A) Increases the internal energy of the gas and increases the temperature of the gas

Q20. The specific heat of water is

(A) 1.817
(B) 2512
(C) 4.187
(D) None of these

Answer: (C) 4.187

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