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# Quiz: Mechanical Engineering 24th May

Quiz: Mechanical Engineering
Exam: DFCCIL
Topic: Basic Thermodynamics

Each question carries 2 mark
Negative marking: 1/3 mark
Time: 10 Minutes

Q1. The standard fixed point of thermometry is
(a) Ice point
(b) Sulphur point
(c) Triple point of water
(d) Normal boiling point of water

Q2. Two blocks which are at different states are brought into contact with each other and allowed to reach a final state of thermal equilibrium. The temperature is specified by the
(a) Zeroth law of thermodynamics
(b) First law of thermodynamics
(c) Second law of thermodynamics
(d) Third law of thermodynamics

Q3. The integrating factor of reversible heat transfer is
(a) 1/T
(b) 1/P
(c) 1/V
(d) P/T

Q4. Heat transferred to a closed stationary system at constant volume is equal to
(a) work transfer
(b) increase in internal energy
(c) increase in enthalpy
(d) increase in Gibbs function

Q5. Which among the following is not a boundary phenomenon?
(a) Work transfer
(b) Heat transfer
(c) Mass transfer
(d) Change of temperature

Q6. A piston cylinder device with air at an initial temperature of 28℃ undergoes an expansion process for which pressure and volume are related as given below:
P (kPa) 200 100 80 54 30
V (m^3) 0.2 0.3 0.4 0.5 0.8
(Given: ln2=0.693 ,ln3=1.098)
What is the work done by the system?
(a) 9 kJ
(b) 22.85 kJ
(c) 11 kJ
(d) 12 kJ

Q7. In free expansion process
(a) W_(1-2)=0
(b) Q_(1-2)=0
(c) dU = 0
(d) All of the above

Q8. Thermodynamic work is the product of
(a) Two intensive properties
(b) Two extensive properties
(c) An intensive property and change in an extensive property
(d) An extensive property and change in intensive property

Q9. The maximum amount of mechanical energy that can be converted into heat in any process
(a) depends on source and sink temperature
(b) depends on friction present
(c) depends on nature of mechanical energy
(d) is 100%

Q10. The expression for work done during a process ∫▒pdV is applicable for
(a) reversible process only
(b) irreversible process only
(c) polytropic process only
(d) any process

Solutions

S1. Ans (c)
Sol. The standard fixed point of thermometry is triple point of water (273.16 ℃).

S2. Ans (a)
Sol. If two blocks are in thermal equilibrium with each other then temperature of the blocks is specified by Zeroth law of thermodynamics.

S3. Ans (a)
Sol. We know that
Change in entropy due to reversible heat transfer in a closed system dS=dQ/T
Here, change in heat transfer (dQ) is an inexact differential and can be made exact by multiplying it with integrating factor 1/T.

S4. Ans (b)
Sol. From first law of thermodynamics for closed stationary system,
∆Q=∆U+PdV.
For constant Volume dV=0,
So, ∆Q=∆U (Change in internal energy)

S5. Ans (d)
Sol. Heat transfer, mass transfer and work transfer all are boundary phenomenon.

S6. Ans (b)
Sol.
First calculate polytropic index (n),
Comparing 1st and 2nd state from PV^n=C
P_1 V_1^n=P_2 V_2^n.
200.〖0.2〗^n=100.〖0.3〗^n
Taking ln
We get, n=1.7
So, Work done by the system=(P_1 V_1-P_2 V_2)/(n-1)
W=(200X0.2-30X0.8)/(1.7-1)
W=22.85 kJ

S7. Ans (d)
Sol. Free expansion process is basically an expansion process against vacuum.
In this process there is no heat transfer & work transfer from & to the system, so as a result temperature before & after expansion is constant and internal energy remains constant.

S8. Ans (c)
Sol. Work done =∫▒PdV
P = Intensive property
dV =Change in extensive property

S9. Ans (d)
Sol. According to first law of thermodynamics for a process,
ΣQ=ΣW.
According to second law of thermodynamics, high grade energy (work or mechanical energy) can be completely converted into low grade energy (heat). But its reverse is not viable.

S10. Ans (a)
Sol. Work done by a closed system in a reversible process = ∫▒pdV

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