Seatwork 1 Problems

Republic of the Philippines
CAMARINES SUR POLYTECHNIC COLLEGES

Nabua, Camarines Sur
NAME: ________________________________ Section: _______________ Exam No. _________
1. A 4 kg/s of water at 40˚C is mixed with 6 kg/s of water at 100˚C in a steady flow process. If the resulting
temperature of resulting mixture is 76˚C, determine the change in entropy.
A. 1.23 kJ/s-K
B. 0.152 kJ/s-K
C. Zero kJ/s-K
D. 2.311 kJ/s-K
2. Find the enthalpy of Helium if its internal energy is 200 kJ/kg.
A. 144 kJ/kg
B. 223.42 kJ/kg
C. 333.42 kJ/kg
D. 168 kJ/kg
3. The kinetic energy of a body of a mass 2 kg, when it falls in air from rest through a height of 5m is
___________.
A. 98.1 J
B. 9.8N
C. 10 N
D. 50 J
4. A gas contained in a cylinder is compressed, the work required for compressing being 5000 kJ. During
the process, heat interaction of 2000 kJ causes the surrounding to be heated. The change in internal
energy of the gas during the process is _____________.
A. -7000 kJ
B. -3000 kJ
C. +3000 kJ
D. +7000 kJ
5. A perfect gas has a value of R = 58.8 ft-lb/lb-R and k = 1.26. If 20 Btu are added to 10 lbs of this gas at
constant volume when initial temperature is 90˚F, find the final temperature.
A. 97˚F
B. 104˚F
C. 154˚F
D. 185˚F
6. For a steady flow process from state 1 to 2, enthalpy changes from h1 = 400 kJ/kg to h2 = 100 kJ/kg and
entropy changes from s1 = 1.1 kJ/kg-K to s2 = 0.7 kJ/kg-K. Surrounding environmental temperature is 300
K. Neglect changes in kinetic and potential energy. The change in availability of the system is _________.
A. 420kJ/kg
B. 300kJ/kg
C. 180kJ/kg
D. 190 kJ/kg
7. Steam enters a turbine stage with an enthalpy of 3620 KJ/kg at 75 m/s and leaves the same stage with
an enthalpy of 2800 KJ/kg at 128 m/s. Calculate the work done by the steam.
A. 514.62 KJ/kg
B. 614.62 KJ/kg
C. 714.62 KJ/kg
D. 814.62 KJ/kg
8. One hundred grams of water is mixed to 150 grams of alcohol (density=790 kg/m3). Calculate the
specific volume of the solution assuming that it is mixed completely.
A. 1.2 cm3/gm
B. 1.5 cm3/gm
C. 1.75 cm3/gm
D. 2.0 cm3/gm
9. The mass flow rate of the gas in a gas turbine is 40 kg/sec. The specific enthalpy and velocity in the inlet
are 1300 KJ/kg and 160 m/sec respectively while in the outlet are 350 KJ/kg and m/sec respectively.
Calculate the power output in KW of the turbine if there is a heat loss of 1000 KW.
A. 37462
B. 34605
C. 41872
D. 30405
10. What is the specific volume of air at 15 psia and 90˚F in ft3/lb?
A. 13.57 ft3/lb
B. 15.57 ft3/lb
C. 17.57 ft3/lb
D. 19.57 ft3/lb
11. Find the mass of carbon dioxide having a pressure of 20 psia at 200˚F with 10 ft3 volume.
A. 1.04 lbs
B. 1.14 lbs
C. 1.24 lbs
D. 1.34 lbs
12. Which of the following is an extensive property of a thermodynamic system?
A. Volume
B. Pressure
C. Temperature
D. Density
13. A 4 kg/s of water at 40˚C is mixed with 6 kg/s of water at 100˚C in a steady flow process. The
temperature of resulting mixture is _____________.
A. 76˚C
B. 87˚C
C. 91˚C
D. 56˚C
14. In a gas turbine, the gases enter the turbine at the rate of 5 kg/s with a velocity of 50 m/s and enthalpy
of 900 kJ/s and leave the turbine with 150 m/s and enthalpy of 400 kJ/kg. The loss of heat from the gases
to the surrounding is 25 kJ/kg. Assume R=0.285 kJ/kg-K and Cp = 1.004 kJ/kg-K. The inlet conditions to be
at 100 kPa and 27˚C. Work transfer is ___________.
A. 2325 kW
B. 4202 kW
C. 3829 kW
D. 1875 kW
15. A 4 kW, 20 L water heater is switched on for 10 min. The heat capacity (Cp) for water is 4.187 kJ/kg-K.
Assuming total electrical energy has gone into heating the water. The increase of the water temperature
is ___________.
A. 15 C˚
B. 25.2 C˚
C. 28.66 C˚
D. 33 C˚
16. A fluid flows through 20 tubes on a single cooler with a velocity of 5 mps. The tube inside diameter is
40 mm and a fluid density of 0.80 gram/ML. What is the volume flow rate in gpm?
A. 996
B. 1075
C. 1394
D. 1992
17. A vessel has a pressure of 200 Kpag. The atmospheric pressure is 10 m of water equivalent. Find the
absolute pressure in m of water.
A. 28.39 m of H2O
B. 30.39 m of H2O
C. 32.39 m of H2O
D. 34.39 m of H2O
18. An air bubble from the bottom of lake becomes triple itself as it reaches on the water surface. How
deep is the lake?
A. 10.65 m
B. 15.65 m
C. 20.65 m
D. 25.65 m
19. Oil flow through 16 tubes on a single cooler with a velocity of 2 m/s. The internal diameter of the tube
is 30mm and oil density is 0.85 gm/ml. Find the volume flow rate in liters per sec.
A. 22.62
B. 32.22
C. 62.22
D. 42.62
20. An engineer carried an aneroid Barometer from the ground floor to his office atop the Shangri-La Hotel
in Mandaluyong City. On the ground level, the barometer reads 102.5 Kpa absolute; topside it read 95 kpa
absolute. Assuming that the average air density was 1.2 kg/m3, estimate the height of the hotel.
A. 500 m
B. 550 m
C. 580 m
D. 637 m
21. Consider 1 kg of air at 32˚C that expanded by a reversible polytropic process with n=1.25 until the
pressure is halved. Determine the heat transfer. Specific heat at constant volume for air is 0.7186 kJ/kg.K.
A. 17.02 kJ heat rejected
B. 17.02 kJ heat added
C. 7.05 kJ heat rejected
D. 7.05 kJ heat added

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Republic of the Philippines

CAMARINES SUR POLYTECHNIC COLLEGES

NAME: ________________________ Section: _ Exam No. ___

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