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Thermodynamics Reviewer 3

  1. A gas initially at 20 psia and 1.5 cu ft undergoes a process to 100 psia and .50 cu ft during which the enthalpy  increases by 15.5 Btu; Cv = 2.44 Btu/lb*R. Determine (a) dU, (b) Cp, and (c) R.  

2. A Centrifugal pump operating under steady flow conditions delivers 2,270 kg/min of water (water rho= 1000 kg/m^3)  from an initial pressure of 82,740 Pa to a final pressure of 275,800 Pa. The diameter of the inlet pipe to the pump is  15.24 cm and the diameter of the discharge pipe is 10.16 cm. What is work in (kJ/min)? Assume mass is equal to  1kgm, and mass flow rate = (density x area x velocity). 

a. W=-201.7933 kJ/min 

b. W=-458.0709 kJ/min 

c. W=275.7933 kJ/min 

d. W=490.0709 kJ/min 

3. A skydiver brought a mercury barometer for his experiment. The barometer reads 654mm before he jumps, after  landing at sea level the barometer reading goes down to 480mm. At what altitude does the skydiver jumps? Assuming  the specific weight of air is 12N/m3 and Specific Gravity of Mercury is 13.6. 

Ans. h = 1933.86152 m 

4. What average force is necessary to stop a landing gear with a mass of 1.5kg and rolling at a speed of 30m/s as it  dents the wall 5cm deep after hitting? 

Ans. F = 13500 N 

5. Air at 100 kPa and 280 K is compressed steadily to 600 kPa and 400 K. The mass flow rate of the air is 0.02 kg/s,  and a heat loss of 16 kJ/kg occurs during the process. Assuming the changes in kinetic and potential energies are  negligible, determine the necessary power input to the compressor. 

Ans. Wsf = 2731.472 W

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