1. Name the forms of energy transfer across the boundary of a
thermodynamic system.
2. State the
thermodynamics definition of work.
3. Displacement work is
not applicable to _____________ systems.
4. The
polytropic index n of process can be represented by
a) n = b) n = c) n =
choose the right
answer.
5. What are point and
path functions? Give examples.
6. What is meant by
displacement work?
7. What is meant by an
indicator diagram?
8. Define mean effective
pressure.
9. What are the modes of
heat transfer?
10. A
certain fluid expands in a quasi-static process from 0.1 m3 to 0.8 m3 at a constant pressure of
1000 kPa. Find the work done. [700 kJ]
11. Zeroth law of
thermodynamics is the basis of _______________________
a) Temperature
measurement c) Heat
measurement
b) Pressure
measurement d)
Internal energy
e) Enthalpy
Choose the correct
answer
12. Mass remains constant
for a closed system (T / F)
13. What are the
similarities between work and heat?
14. Calculate the work required
to lift a 25 kg body from an elevation of 200 m above mean sea level to an elevation of 300 m in 2 minutes. [24.525 kJ]
15. What is the work done
in compressing a spring of stiffness 500 N/cm by 2 cm?
[1 kJ]
16. An electric water with
a resistance of 50 Ohms heater is connected across a power
supply of 240 Volt for a period of 1 hour.
a) Determine the work
done by the power source on the heater.
b) How many units of
electricity are consumed?
[5184 kJ; 1.44 k Whr]
17. A gas is contained in a piston cylinder
arrangement as given in the Figure 2.28.Initial volume of the gas is 0.5 m3. It is compressed from 1
bar to 10 bar such that the temperature remains constant. Find the final volume
and work done.
[0.05
m3 ; -115.13 kJ]
18. Air expands from 0.1 m3 to 0.23 m3 at a constant temperature of
50oC.
Calculate the work done per kg of air.
Rair = 0.287 kJ/kgK.
[77.2
kJ]
19. Oxygen contained in a
cylinder fitted with a piston expands in a quasistatic process according to the
law pV1.5 = constant. The initial
pressure, temperature and volume are 5 bar, 300 k and 0.05 m3. After expansion, the
pressure is 2 bar.
Find
the following :
a.
Final volume
b.
Final temperature
c.
Work done
[0.0921 m3 ; 221 K ; 13.16 kJ]
20. Air is compressed
adiabatically from 0.92 m3 to 0.29
m3 in a piston cylinder
arrangement. Taking its initial pressure and temperature as 103 kPa and 300 k
respectively, find the work done. Also
find the final temperature.
[-139.04 kJ ; 476
K]
21. A spherical balloon
has a diameter of 25 cm and contains air at a pressure of 150 kPa. The diameter of the balloon increases to 30
cm because of heating, and during this process, the pressure is proportional to
the diameter. Calculate the work done on
the gas assuming reversible work interaction.
[0.989 kJ]
22. A
bicycle pump has a total stroke of 25 cm and is used to pump air into a tyre
against a pressure of 3.5 bar. Calculate the length stroke necessary before air
enters the tyre when the piston is pushed in
a) rapidly
b) slowly
Assume
atmospheric pressure is 1 bar.
[17.0 cm ; 17.9 cm]
23. A mass of air
occupying 0.5 m3 at 2
bar and 200oC is compressed reversibly and adiabatically
to 5 bar and then it undergoes isobaric expansion so that it gives out 45 kJ of
work. If the system is to be brought back to its initial state what should be
the polytropic index ? calculate the network interaction of this cycle. Sketch
the cycle on a p-V diagram. Also compute the power developed if the number of
cycles executed per minute is 300.
[2.57 ; 17.8 kJ ; 88.9
kW]
24. It
is required to lift five people on an elevator through a height of 100 m. The
work required is found to be 341.2 kJ and the gravitational acceleration is
9.75 m/s2. Determine the average mass per person.
[69.95
kg]
25. What
is the work required to accelerate a vehicle of mass 500 kg from rest to a
velocity of 60 kmph.
[69.44 kJ]
26. The indicator card of
an 8 cm bore, 10 cm stroke water pump is in the shape of a rectangle of
dimension 2 ´ 10 cm. The indicator spring constant is 22
MPa/m.
a) Find the mean effective pressure.
b)
If the cycle is repeated once in every
second, what is the power required by the pump?
[440 kPa
; 0.22 kW]
27. A
quantity of a substance in a closed vessel is undergoing a reversible process in such
a way that the pressure is proportional to the square roof of volume from 1 m3 to 2m3. The initial pressure is 100 KPa. Compute the work done.
[2.33 kJ]
28. A
cylinder of 8 cm internal diameter is fitted with a piston loaded by a coil
spring of stiffness 140 N/cm of compression. The cylinder
contains 0.0005m3 of air
at 15°C and 3 bar. Find the work done when the piston moves by 4 cm as
the gas expands.
[ 7.11 J]
29. Carbondioxide
is taken in a piston cylinder arrangement such that it occupies a volume
of 1m3 at 1
bar and 27°C. It has to be compressed to 0.2 m3 such that the temperature remains constant
during compression. Compute the workdone and final
pressure.
[-160.94 kJ;
500 kPa]
30. 5
kg of oxygen initially at 10 bar, 370 K is undergoing expansion to 1 bar. If
the final temperature is 300K. Determine the
following:
a)
Initial volume
b)
Final volume
c)
Polytropic index
d)
Work done
Take
the molecular weight of oxygen as 32.
[0.48m3 ;
3.897m3 ; 1.1 ;
903 kJ]
31. A
rigid container of volume 0.4 m3 is filled with oxygen until the pressure
reaches 1200 kPa.
It is then cooled so that the pressure reduces to 900 kPa. How much work is performed ? Draw
a p-V diagram for the process.
[0 kJ]
32. A
paddle wheel supplies work to a system at the rate of 80 W. During a period of 1
minute the system expands from 0.03 m3 to 0.08 m3 against a constant pressure of
500 kPa. Find the net work interaction during this period of 1 minute.
Ans : [20.2 kJ]
33. 1
Kg of air undergoes expansion from 800 kPa, 300 K to 120 kPa in such a way that
p(v + 0.2) = Constant, where p is the pressure in kPa and v is the specific volume in m3/Kg. Find the work done in the process.
Ans : [466.88 kJ]
