1. A piston-cylinder device initially contains air at 150 kPa and 27°C. At this state, the volume is 400 litre. The mass of the piston is such that a 350 kPa pressure is required to move it. The air is now heated until its volume has doubled. Determine work done by the air.
a) 120 kJ
b) 130 kJ
c) 100 kJ
d) 140 kJ
Explanation: Work done = P3(V3- V1) = 140 kJ.
2. Find the change in u for carbon dioxide between 600 K and 1200 K for a constant Cv0 value.
a) 291.8 kJ/kg
b) 391.8 kJ/kg
c) 491.8 kJ/kg
d) 591.8 kJ/kg
Explanation: Δu = Cv0 ΔT = 0.653 ×(1200–600) = 391.8 kJ/kg.
3. Calculate the change in enthalpy of carbon dioxide from 30 to 1500°C at 100 kPa at constant specific heat.
a) 2237.7 kJ/kg
b) 1637.7 kJ/kg
c) 1237.7 kJ/kg
d) 2337.7 kJ/kg
Explanation: Δh = CpΔT = 0.842 (1500 – 30) = 1237.7 kJ/kg.
4. A sealed rigid vessel has volume of 1 m3 and contains 2 kg of water at 100°C. The vessel is now heated. If a safety pressure valve is installed, at what pressure should the valve be set to have a maximum temperature of 200°C ?
a) 431.3 kPa
b) 531.3 kPa
c) 631.3 kPa
d) 731.3 kPa
Explanation: Initial specific volume (v1) = 1 m3/2 kg = 0.5 m3/kg
Interpolating, pressure for the same specific volume at 200°C
= 400 + {(0.53422-0.5)/(0.53422-0.42492)}*(500-400) = 431.3 kPa.
5. A system undergoing change in state from A to B along path ‘X’ receives 100 J heat and does 40 J work. It returns to state A from B along path ‘Y’ with work input of 30 J. Calculate the heat transfer involved along the path ‘Y’.
a) – 60 J
b) 60 J
c) – 90 J
d) 90 J
Explanation: ∆UX = AQB – AWB = 100 – 40 = 60 J
Heat transfer involved along the ‘Y’ (BQA) = ∆UY + BWA = – ∆UX + BWA
= – 60 – 30 = – 90 J.
6. When a body A is in thermal equilibrium with a body B, and also separately with a body C, then B and C will be in thermal equilibrium with each other.
a) True
b) False
Explanation: Zeroth law of thermodynamics.
7. Which of the following were used as fixed points before 1954?
a) The ice point
b) The steam point
c) All of the mentioned
d) None of the mentioned
Explanation: Both of these were used.
8. What is the standard fixed point of thermometry?
a) The ice point
b) The steam point
c) The triple point of water
d) None of the mentioned
Explanation: After 1954, only one fixed point has been used.
9. All gases and vapours approach ideal gas behaviour at?
a) High pressure and high density
b) Low pressure and low density
c) High pressure and low density
d) Low pressure and high density
Explanation: Comes from ideal gas equation of state.
10. The value of ratio of the steam point temperature to the ice point temperature is?
a) 1.466
b) 1.266
c) 1.166
d) 1.366
Explanation: This value is a universal constant.