Mechanical Engineering Thermodynamics – Set 07

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Q1. Temperature of a gas is produced due to

(A) Its heating value
(B) Kinetic energy of molecules
(C) Repulsion of molecules
(D) Surface tension of molecules

Answer: (B) Kinetic energy of molecules

Q2. Specific heat of air at constant pressure is equal to

(A) 0.17
(B) 0.21
(C) 0.24
(D) 1.0

Answer: (C) 0.24

Q3. The statement that molecular weights of all gases occupy the same volume is known as

(A) Avogadro’s hypothesis
(B) Dalton’s law
(C) Gas law
(D) Law of thermodynamics

Answer: (A) Avogadro’s hypothesis

Q4. According to Avogadro’s law

(A) The product of the gas constant and the molecular mass of an ideal gas is constant
(B) The sum of partial pressure of the mixture of two gases is sum of the two
(C) Equal volumes of all gases, at the same temperature and pressure, contain equal number of molecules
(D) All of the above

Answer: (C) Equal volumes of all gases, at the same temperature and pressure, contain equal number of molecules

Q5. Work done is zero for the following process

(A) Constant volume
(B) Free expansion
(C) Throttling
(D) All of the above

Answer: (D) All of the above

Q6. In order that a cycle be reversible, following must be satisfied

(A) Free expansion or friction resisted expansion/compression process should not be encountered
(B) When heat is being absorbed, temperature of hot source and working substance should be same
(C) When beat is being rejected, temperature of cold source and working substance should be same
(D) All of the above

Answer: (D) All of the above

Q7. In an irreversible process, there is a

(A) No loss of heat
(B) Loss of heat
(C) Gain of heat
(D) No gain of heat

Answer: (B) Loss of heat

Q8. 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) 84 kJ
(C) 54 kJ
(D) 114 kJ

Answer: (C) 54 kJ

Q9. Otto cycle efficiency is higher than Diesel cycle efficiency for the same compression ratio and heat input because in Otto cycle

(A) Heat rejection is lower
(B) Expansion and compression are isentropic
(C) Combustion is at constant volume
(D) Maximum temperature is higher

Answer: (A) Heat rejection is lower

Q10. The efficiency of Joule cycle is

(A) Less than Carnot cycle
(B) Equal to Carnot cycle
(C) Greater than Carnot cycle
(D) None of these

Answer: (A) Less than Carnot cycle

Q11. The term N.T.P. stands for

(A) Nominal temperature and pressure
(B) Natural temperature and pressure
(C) Normal temperature and pressure
(D) Normal thermodynamic practice

Answer: (C) Normal temperature and pressure

Q12. Measurement of temperature is based on

(A) Thermodynamic properties
(B) Zeroth law of thermodynamics
(C) First law of thermodynamics
(D) Second law of thermodynamics

Answer: (B) Zeroth law of thermodynamics

Q13. For same compression ratio and for same heat added

(A) Otto cycle is more efficient than Diesel cycle
(B) Diesel cycle is more efficient than Otto cycle
(C) Efficiency depends on other factors
(D) Both Otto and Diesel cycles are equally efficient

Answer: (A) Otto cycle is more efficient than Diesel cycle

Q14. The efficiency of Diesel cycle with decrease in cut-off

(A) Increases
(B) Decreases
(C) First increases and then decreases
(D) First decreases and then increases

Answer: (A) Increases

Q15. The unit of mass in S.I. units is

(A) Kilogram
(B) Gram
(C) Tonne
(D) Quintal

Answer: (A) Kilogram

Q16. According to kinetic theory of gases, the absolute zero temperature is attained when

(A) Volume of the gas is zero
(B) Pressure of the gas is zero
(C) Kinetic energy of the molecules is zero
(D) Specific heat of gas is zero

Answer: (C) Kinetic energy of the molecules is zero

Q17. Characteristic gas constant of a gas is equal to

(A) Cp /Cv
(B) Cv /Cp
(C) Cp – Cv
(D) Cp + Cv

Answer: (C) Cp – Cv

Q18. To convert volumetric analysis to gravimetric analysis, the relative volume of each constituent of the flue gases is

(A) Divided by its molecular weight
(B) Multiplied by its molecular weight
(C) Multiplied by its density
(D) Multiplied by its specific weight

Answer: (B) Multiplied by its molecular weight

Q19. The value of n = 1 in the polytropic process indicates it to be

(A) Reversible process
(B) Isothermal process
(C) Adiabatic process
(D) Irreversible process

Answer: (B) Isothermal process

Q20. For which of the following substances, the gas laws can be used with minimum error

(A) Dry steam
(B) Wet steam
(C) Saturated steam
(D) Superheated steam

Answer: (D) Superheated steam

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