Mechanical Engineering Thermodynamics – Set 14

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Q1. The efficiency of Diesel cycle increases with

(A) Decrease in cut-off
(B) Increase in cut-off
(C) Constant cut-off
(D) None of these

Answer: (A) Decrease in cut-off

Q2. The atomic mass of sulphur is

(A) 12
(B) 14
(C) 16
(D) 32

Answer: (D) 32

Q3. The general gas energy equation is (where Q1 – 2 = Heat supplied, dU = Change in internal energy, and W1 – 2 = Work done in heat units)

(A) Q1 – 2 = dU + W1 – 2
(B) Q1 – 2 = dU – W1 – 2
(C) Q1 – 2 = dU/W1 – 2
(D) Q1 – 2 = dU × W1 – 2

Answer: (A) Q1 – 2 = dU + W1 – 2

Q4. The sum of internal energy (U) and the product of pressure and volume (p.v) is known as

(A) Work-done
(B) Entropy
(C) Enthalpy
(D) None of these

Answer: (C) Enthalpy

Q5. Otto cycle consists of

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

Answer: (A) Two constant volume and two isentropic processes

Q6. The reading of the pressure gauge fitted on a vessel is 25 bar. The atmospheric pressure is 1.03 bar and the value of ‘g’ is 9.81 m/s2. The absolute pressure in the vessel is

(A) 23.97 bar
(B) 25 bar
(C) 26.03 bar
(D) 34.81 bar

Answer: (C) 26.03 bar

Q7. Second law of thermodynamics defines

(A) Heat
(B) Work
(C) Internal energy
(D) Entropy

Answer: (D) Entropy

Q8. The behavior of a perfect gas, undergoing any change in the variables which control physical properties, is governed by

(A) Boyle’s law
(B) Charles’ law
(C) Gay-Lussac law
(D) All of these

Answer: (D) All of these

Q9. The atomic mass of oxygen is

(A) 8
(B) 18
(C) 16
(D) 32

Answer: (C) 16

Q10. The throttling process is __ process.

(A) Reversible
(B) Irreversible
(C) Reversible or irreversible
(D) None of these

Answer: (B) Irreversible

Q11. The amount of heat required to raise the temperature of 1 kg of water through one Kelvin is called

(A) Specific heat at constant volume
(B) Specific heat at constant pressure
(C) kilo-Joule
(D) None of these

Answer: (C) kilo-Joule

Q12. The __ states that change of internal energy of a perfect gas is directly proportional to the change of temperature.

(A) Boyle’s law
(B) Charle’s law
(C) Gay-Lussac law
(D) Joule’s law

Answer: (D) Joule’s law

Q13. Which of the following is the correct statement?

(A) For a given compression ratio, both Otto and Diesel cycles have the same efficiency
(B) For a given compression ratio, Otto cycle is more efficient than Diesel cycle
(C) For a given compression ratio, Diesel cycle is more efficient than Otto cycle
(D) The efficiency of Otto or Diesel cycle has nothing to do with compression ratio

Answer: (B) For a given compression ratio, Otto cycle is more efficient than Diesel cycleAnswer: (C) Pulverized coal

Q14. The fuel mostly used in cement industry and in metallurgical processes is

(A) Wood charcoal
(B) Bituminous coke
(C) Pulverized coal
(D) Coke

Answer: (C) Pulverized coal

Q15. For the same compression ratio, the efficiency of Diesel cycle is __ Otto cycle.

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

Answer: (B) Less than

Q16. An adiabatic process is one in which

(A) No heat enters or leaves the gas
(B) The temperature of the gas changes
(C) The change in internal energy is equal to the mechanical work-done
(D) All of the above

Answer: (D) All of the above

Q17. The efficiency of Carnot cycle depends upon

(A) Temperature limits
(B) Pressure ratio
(C) Volume compression ratio
(D) Cut-off ratio and compression ratio

Answer: (A) Temperature limits

Q18. The natural solid fuel is

(A) Wood
(B) Coke
(C) Anthracite coal
(D) Pulverized coal

Answer: (A) Wood

Q19. The state of a substance whose evaporation from its liquid state is complete, is known as

(A) Vapour
(B) Perfect gas
(C) Air
(D) Steam

Answer: (B) Perfect gas

Q20. The efficiency of a gas turbine is given by

(A) (Net work output)/(Work-done by the turbine)
(B) (Net work output)/(Heat supplied)
(C) (Actual temperature drop)/(Isentropic temperature drop)
(D) (Isentropic increase in temperature)/(Actual increase in temperature)

Answer: (B) (Net work output)/(Heat supplied)

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