Thermodynamics 3

PROBLEMS:

1.If air is at pressure, p, of 3200 lbf/ft^2, and at a temperature, T, of 800 ˚R, What is the specific volume, v? (R=5303 ft-lbf/lbm-˚R, and air can be modeled as an ideal gas.) A.9.8 ft^3/lbm B.11.2 ft^3/lbm C.13.33 ft^3/lbm D.14.2 ft^3/lbm Formula: pv = RT

v = RT / p

ans. C 2. Steam at 1000 lbf/ft^2 pressure and 300˚R has specific volume of 6.5 ft^3/lbm and a specific enthalpy of 9800 lbf-ft/lbm. Find the internal energy per pound mass of steam. A.2500 lbf-ft/lbm B.3300 lbf-ft/lbm C.5400 lbf-ft/lbm D.6900 lbf-ft/lbm Formula: h = u + pV

u = h – pV

ans. B 3. 3.0 lbm of air are contained at 25 psia and 100 ˚F. given that Rair = 53.35 ft-lbf/lbm˚F, what is the volume of the container? A.10.7 ft^3 B.14.7 ft^3 C.15 ft^3 D.24.9 ft^3 Formula: use the ideal gas law pV = mRT T = (100 + 460) ˚R V = mRT / p ans.

D

4. The compressibility factor, x, is used for predicting the behavior of non-ideal gases. How is the compressibility factor defined relative to an ideal gas? (subscript “c” refers to critical value) A. z = P / Pc B. z = pV / RT C. z = T / Tc D. z = RT / pV Hint: for an real gases the compressibility factor, x, is an dimensionless constant given by pV= zRT. Therefore z = pV / RT ans.

B

5. From the steam table , Determine the average constant pressure specific heat (c) of steam at 10 kPa and 45.8 ˚C A.1.79 kJ/ kg-˚C B.10.28 kJ/ kg-˚C C.30.57 kJ/ kg-˚C D. 100.1 kJ/ kg-˚C Formula: �h = c�T From the steam table At 47.7 ˚C At 43.8 ˚C

ans.

h= 2588.1 kJ/ kg h= 2581.1 kJ/ kg

A

6. A 10m^3 vessel initially contains 5 m^3 of liquid water and 5 m^3 of saturated water vapor at 100 kPa. Calculate the internal energy of the system using the steam table. A. 5 x10^5 kJ B. 8 x10^5 kJ C. 1 x10^6 kJ D. 2 x10^6 kJ Formula: from the steam table vƒ = 0.001043 m^3 / kg vg = 1.6940 m^3 / kg u ƒ = 417.3 kJ/kg ug = 2506 kJ/kg formula: M vap = V vap/vg M liq = V liq/ vƒ u = uƒ M liq + ug M vap ans. D

7. A vessel with a volume of cubic meter contains liquid water and water vapor ion equilibrium at 600 kPa. The liquid water has mass of 1kg. using the steam table, calculate the mass of the water vapor. A. 0.99kg B. 1.57 kg C. 2.54 kg D.3.16 kg Formula: from the steam table at 600 kPa vƒ = 0.001101 m^3 / kg vg = 0.3157 m^3 / kg

ans. D

Vtot = mƒ vƒ + mg vg mg = (tot- mƒ vƒ) / vg ans.D

8.Calculate the entropy of steam at 60 psiawith a quality of 0.8 A. B. C. D.

0.4274 BTU/lbm-˚R 0.7303 BTU/lbm-˚R 1.1577 BTU/lbm-˚R 1.2172 BTU/lbm-˚R

Formula: from the steam table at 60 psia: sƒ = 0.4274 BTU/lbm-˚R sƒg = 1.2172 BTU/lbm-˚R) s = sƒ + x sƒg where x = is the quality ans.

C

9. Find the change in internal energy of 5 lbm of oxygen gas when the temperature changes from 100 ˚F to 120 ˚F. cv= 0.157 BTU/lbm-˚R A.14.7 BTU B.15.7 BTU C. 16.8 BTU D. 15.9 BTU Formula: �U= mcv�T Ans. B

10. Water (specific heat cv= 4.2 kJ/ kg · K ) is being heated by a 1500 W heater. What is the rate of change im temperature of 1kg of the water? A. 0.043 K/s B. 0.179 K/s C. 0.357 K/s D. 1.50 K/s Formula: Q = mcv ( �T) Ans.

B

11. A system weighing 2 kN. Determine the force that accelerate if to 12 m/s^2. a. vertically upward when g= 9.7 m/s^2 A. 4474.23 N B.5484.23 N C.4495.23 N D.5488.23 N Formula: F = m/k (a +g) ans.

A

12. refer to problem # 11. determne the force that accelerates if to 12 m/s^2.horizontally along a frictionless plane. A.2474.23 N B.2574.23 N C.3474.23 N D.2374.23 N Formula : M = wk / g F = ma / k ans. A 13. A problem Drum ( 3 ft dia ; 6 ft height ) is field with a fluid whose density is 50 lb/ft^3 Determine the total volume of the fluid.

A. 42.41 ft^3 B.44.35 ft^3 C.45.63 ft^3 D.41.23 ft^3 Formula: Vf = (pi d^2 h) / 4 ans. A

14. What is the resulting pressure when one pound of air at 15 psia and 200 ˚F is heated at constant volume to 800 ˚F. A.15 psia B.28.6 psia C.36.4 psia. D.52.1 psia Formula : T1/p1 = T2/p2 p2 = p1T2 / T1 ans.B 15. What horsepower is required to isothermally compress 800 ft^3 of Air per minute from 14.7 psia to 120 psia? A. 28 hp B.108 hp C.256 hp D.13900 hp] Formula: W= p1V1 ln (p1/p2) Power = dW / dt ans. B 16. What is the equation for the work done by a constant temperature system? A. W = mRT ln(V2-V1) B. W = mR ( T2-T1 ) ln( V2/V1) C. W = mRT ln (V2/V1) D. W = RT ln (V2/V1)] Formula : W=∫ pdV lim 1,2 р = mRT / V ans. C 17. Twenty grams of oxygen gas are compressed At a constant temperature of 30 ˚C to 5% of their original volume. What work is done on the system. A.824 cal B.924 cal C.944 cal D.1124 cal

Formula: W = -mRT ln (V2/V1) Where R = (1.98 cal/gmole ·K) (32 g/gmole) ans.

D

18. Helium ( R= 0.4698 BTU/lbm-˚R ) is compressed isothermally from 14.7 psia and 68 ˚F. The compression ratio is 1:4. Calculate the work done by the gas. A. –1454 BTU/lbm B.-364 BTU/lbm C.-187 BTU/lbm D.46.7 BTU/lbm Formula: W = RT ln (V2/V1) ans.B 19.Gas is enclosed in a cylinder with a weighted piston as the stop boundary. The gas is heated and expands from a volume of 0.04 m^3 to 0.10 m^3 at a constant pressure of 200kPa.Calculate the work done by the system. A. 8 kJ B. 10 kJ C.12 kJ D.14 kJ Formula: W = p (V2-V1) ans.C 20. refer to problem no.13. Determine the specific volume… A. 0.02 ft^3/lbm B. 0.05 ft^3/lbm C. 1.0 ft^3/lbm D. 1.2 ft^3/lbm Formula : Vf = ( pi d^2 h) / 4 Pf = mf / vf Specific volume= Vf / mf ans.

A

21.What is the weight of a 66-kg m man at standard condition? (Formula: Fg = mg / k) a. 66 kgf b. 66 kgm c. 66 lb m d. 66 gf a

22.What is the specific weight of ater at standard condition? (Formula: γ = ρg / k) a. 1000 kgm /m3 b. 9.8066 m/s 2 3 c. 1000 kg /m f d. None of the above c

23.7 23 .746 46 °R = ____ __ ____ __ °F a. 254 b. 345 c. 286 d. None of the above c

24.A 30-m vertical column of fluid (density 1878 kg/m 3) is located where g= 9.65 mps 2. Find the pressure at t6he base of the column. (Formula: pg = gρhg /k ) a. 543680 N/m 2 b. 543.68 kPa (gage) c. Both a & b d. None of the above c

25.Ten cu ft of air at 300 psia p sia 400° 400 °F is cooled coo led to 140°F at constant cons tant volume. volu me. What W hat is the final pressure? (formula: p2 = p1T2 / T1 ) a. 0 b. 209 psia c. - 420 psia d. None of the above b

26.8 26 .876 76 °R = ____ __ ___ _ °F a. 335 b. 416 c. 400 d. None of the above b

27.There are 1.36 kg of gas, for which R = 377 J/kg.k and k=1.25, that undergo a nonflow constant volume process from p 1 = 551.6 kPa and t 1 = 60° 60 °C to t o p 2 = 1655 kPa. During the process the gas is internally stirred and there are also added 105.5 kJ of heat. Determine t 2. (Formula: T2 = T1p2/ p1 ) a. 999 K b. 888 K c. 456K d. One of the above a

28.5 atm = ____ mmHg a. 8300 b. 3800 c. 3080 d. None of the above b

29.A certain gas, with c p = 0.529 Btu/lb.° Bt u/lb.°R and R = 96.2 ft.lb/lb.° ft .lb/lb.°R, expand expan d s from 5 cu ft and 80 °F to 15 cu ft f t while the pressure remains co nstant at 15.5 psia. Compute for T 2. (Formula: T2 = T1V2 / V1 ) a. 46 4 60 °R b. 27 2 70 °R c. 1620 16 20 °R d. None of the above c

30.In the above problem, compute for the mass. (Formula: m = p1V1 / RT1 ) a. 0.2148 lb b. 0.2134 lb c. 0.1248 lb d. None of the above a

31.7 31 .710 10° °R= ____ __ ____ __ °C a. 214 b. 121 c. 213 d. None of the above b

32.2 32 .212 12 °F = ____ __ ___ _ °C a. 200 b. 150 c. 100 d. None of the above c

33.Let a closed system execute a state change for which the heat is Q = 100 J and work is W = -25 J. Find �E. (Formula: �E = Q- W ) a. 125 J b. 123 J c. 126 J d. None of the above a

34.A pressure gage registers 50 psig in a region where the barometer is 14.25 psia. Find absolute pressure in psia, Pa. (Formula; p = p atm atm + p g ) a. 433 kPa b. 443 kPa c. 343 kPa d. None of the above b

35. A mass of 5 kg is 100 m above a given datum where local g = 9.75 m/s 2. Find the gravitational force in newtons. (Formula: Fg = mg/k ) a. 48.75 N b. 50 N c. 45 N d. None of the above a

36. In the above problem, find the potential energy of the mass with respect to datum. (Formula: P = mgz/k ) a. 4875 j b. 0.51 j c. 0.46 j d. None of the above a

37. The combined mass m ass of car and a nd passengers travelling tra velling at 72 km/hr km /hr is 1500 kg. Find the kinetic energy of this combined mass. (Formula: K = m v 2 / 2k ) a. 300 kJ b. 200 kJ c. 500 kJ d. None of the above a

38. 14.696 psia = _____ mmHg m mHg a. 760 b. 1 c. 350 d. None of the above b

39. 212 °C = ____ _ ____ _K a. 485 b. 435 c. 498 d. None of the above a

40.212 40. 212 °F = ____ _ ____ _R a. 567 b. 672 c. 700 d. None of the above b

41.

An automobile autom obile tire has a gauge pressure press ure of 200kpa 200kp a at 0°C assuming assum ing no air leaks and no change of volume of the tire, what is the gauge pressure at 35ºC. a. 298.645 b. 398.109 c. 291.167 d. 281.333 a Pg = Pabs - Patm

42.

43.

44.

45.

An ideal gas at 45psig and 80ºF is heated in the close container to 130ºF. What is the final pressure? a. 65.10psi b. 65.11psi c. 65.23psi d. 61.16psi c P1V1 /T1 = P2V2 /T2; V = Constant A wall of the firebrick has an inside temperature of 313ºF and an outside temperature of 73ºF. What is the difference in the surface temperature in Rankin? a. 70 b. 68 c. 72 d. 94 a ºR = ºF + 460 What is the force required to accelerate a mass of 30kg at a rate of 15m/s². a. 460N b. 380N c. 560N d. 450N d F = ma How much does an object having the mass of 100kg weight in newton. a. 981N b. 991N c. 981.6N d. 980.1N a F = ma

46.

47.

48.

49.

The volume of the gas held at constant consta nt pressure press ure increases 4cm² at 0°C to 5cm². What is the final pressure? a. 68.65ºC b. 68.25ºC c. 70.0 70 .01° 1°C d. 79.1ºC b t2 = T2 – T1 A certain gas with cp = 0.529Btu/lb°R and R = 9 6.2ft/lbºR expands from 5ft and 80ºF to 15ft while the pressure remains constant at 15.5 psia. a. T2 =1.620ºR, ▲H = 122.83 Btu b. T2 = 2°R, ▲H = 122.83 Btu c. T2 = 2.620ºR, ▲H = 122.83 Btu d. T2 = 1°R, ▲H = 122.83 Btu a T2 = V2 (t2)/V1 and ▲H = mcp (T 2-T1) A vacuum is connected to a tank reads 3kpa at a location w/ the barametric pressure reading is 75mmhg. Determined the Pabsolute in the tank a. 70.658kpa b. 68kpa c. 58.78kap d. None of the above a Pabs = Patm - Pvacuum Calculate: a. Mass flow flow rate in in lb/hr. lb/hr. b. The velocity at section 2 in fps a. 800,000lb/hr;625ft/s b. 900,000lb/hr;625ft/s c. 888,000lb/hr;269ft/s d. 700,000lb/hr;269ft/s b m = A1V!/V1

50.

A 600kg hammer of a pile pile driver is lilted 2m the pilling head. What is the change of potential energy? If the hammer is realest. What will be its velocity and the instant if it sticks the pilling? a. 10,772N-m and 5.26m/s b. 13,200N-m and 5.26m/s c. 11,772N-m and 6.26m/s d. 11,772N-m and 5.26m/s

c

▲PE = mgo(▲Z)/gc 51. A bayabas falls from a branch 5m above the ground with what speed in meter per second does it strike the ground assume g = 10m/s². a. 11m/s b. 12m/s c. 13m/s d. 10m/s d

▲KE = mV2/2gc 52. While swimming a depth of 13m in a fresh water lake lak e a fish emits an air bubble of volume 2mm² atmospheric pressure is 100kpa what is the original pressure of the bubble. a. 217.17kpa b. 119kpa c. 326.15kpa d. 210kap a Pabs = Pg + Patm 53. Oxygen at 15ºC 15º C and 10.3Mpa 1 0.3Mpa gauge pressure occupies occu pies 600L. What Wha t is the occupied by the oxygen at 8.28Mpa gauge pressure and 35ºC? a. 789.32L b. 796.32L c. 699L d. 588L b V2 = P1V1 /T1P2 54. Water is flowing through a 1 foot diameter pipe at the rate of 10ft/sec. What is the volume flow rate of water in ft³/sec? a. 7.85 b. 6.85 c. 8.85 d. 5.85 a V = Aν 55. A certain fluid is flowing an a 0.5mx0.3 channel at the rate of 3m/s and has a specific volume of 0.012m³/kg. Determined the mass of water flowing in kg/s. a. 267kg/s b. 378kg/s c. 375kg/s d. 456.5kg/s

c m = Aν /V 56. A gas having a volume of 100ft³ at 27ºC is expanded to 120ft³ by heated at constant pressure to what temperature has it been heated to have this new volume? a. 87C b. 85C c. 76C d. 97C a t2 = T2 – T1 57. Water flow f low to a terminal 3mm diameter and has an average speed sp eed of 2m/s.What is the rate of flow in cubic meter/mm? a. 0.0001m³/min b. 0.076 m³/min c. 0.085 m³/min d. 0.097 m³/min c 58. Water flowing at a 6m/s through a 60mm 60m m pipe is suddenly channeled cha nneled into a 30mm pipe. What is the velocity in the small pipe? a. 34m/s b. 24m/s c. 15m/s d. 27m/s b 59. A vertical column of water will be b e supported supp orted to what height by standard atmospheric pressure. a. 33.9ft b. 45ft c. 67ft d. 25.46ft a ho = Po/Yo

60. A fluid flows in a steady manner between two section in a flow line at section 1: A 1 = 1ft², V 1 = 100fpm, volume1 of 4ft³/lb at sec2: A 2 = 2ft², p = 0.20lb/ft³ calculate the velocity at section 2. a. 625fpm b. 567fpm c. 356fpm d. None of the above a 61. The weight of an object is 50lb. What is its mass at standard condition? a. 50 lbm b. 60 lbm c. 70 lbm d. 80 lbm a

formula: m = Fgk / g

62. A vertical column of water will be supported to what height by standard atmospheric pressure. If the Y w  = 62.4lb/ft 3 po = 14.7 psi. a. 44.9 ft b. 33.9 ft c. 22.9 ft d. 55.9 ft b

formula: ho = po / Yw

63. For a certain gas R= 320J/kg.K and c v= 0.84kJ/kg.Kc . Find k? a. 1.36 b. 1.37 c. 1.38 d. 1.39 c

formula: k= R / c v +1

64. Ten cu.ft of air a ir at 300 psia and an d 400°F is coole cool e d to 140° 140 °F at constant cons tant volume. vo lume. What W hat is the transferred heat? a.-120Btu b. -220Btu c.-320Btu d. -420Btu d

formula: Q= mcv(T2-T1)

65. Utilizing the answer to the previous problem, estimate the overall or average increase in temperature ( ∆T ) of the concrete roof from the energy absorbed from the sun during a 12 hour day. Assume that all of the radiation absorbed goes into heating the roof. The specific heat of concrete is about 900 J/kg, and the density is about 2,300 kg/m3. a. 7.9 °C b. 8.9° 8. 9°C c. 9.9° 9. 9°C d. 10.9 10 .9° °C a

formula: ∆Q = m c ∆T

66. The concrete roof of a house is 10 m by 8 m and 10 cm thick (4"). Estimate the total heat the roof would absorb over the 12 day? a. 1.3 x 10 8 J b 2.3 x 10 8 J c. 3.3 x 10 8 J d. 4.3 x 10 8 J a

formula: ∆Q = ∆Q / ∆t x ∆t

67. The value for the ∆U of a system is -120 J. If the system is known to have absorbed 420 J of heat, how much work was done? a. -540 J b. -640 J c. -740 J d. -840 J a

formula: ∆U = q + w

68. When the pressure on a 1 kg liquid is increased isothermally from 1 bar to 3000 bar the Gibbs free energy increases by 360 kJ. Estimate the density of the liquid. a. 0.66 kg liter -1 b. 0.77 kg liter -1 c. 0.88 kg liter -1 d. 0.99 kg liter -1

b

solution:

69. A car whose whose mass is 2 metric tons is accelerated uniformly from stand hill to 100kmph in 5 sec. Find the driving force in Newton’s. a. 11,120N b. 11,320N c. 11,420N d. 11520N a

formula: F= ma / k

70. An ideal gas of volume 1 liter and pressure 10 bar undergoes a quasistatic adiabatic expansion until the pressure drops to 1 bar. Assume γ   to be 1.4 what is the final volume? a. 3.18 l b. 4.18 l c. 5.18 l d. 6.18 l

c

solution:

71. Two masses, one of the 10kg and the other unknown, are placed on a scale in a region where g = 9.67 m/sec 2. The combined weight of these two masses is 174.06 N. Find the unknown mass in kg. a. 20kg c

b. 19kg

c. 18kg

d. 17kg

formula: m= Fg k / g

72. The flow energy of 5ft 3  of a fluid passing a boundary to a system is 80,000 ft-lb. Determine the pressure at this point. a. 222psi d

b. 333psi

formula: Ef = pV

c. 444psi

d. 111psi

73. Find и for steam at 100psia and 600°F.If h = 1329.6 and v = 6.216 a.1214Btu / lb a

b. 1234 Btu / lb

c. 1342 Btu / lb

d. 1324 Btu / lb

formula: и = h – pv/ J

74. What mass of nitrogen is contained in a 10ft 3 vessel at a pressure of 840 atm and 820°R? Make a computation by using u sing ideal gas equati on. a. 194 lb c

b. 214 lb

c.394 lb

d. 413 lb

formula: m= pV / RT

75. A rotary compressor receives 6m 3 / min of a gas (R=410J / kgK, c p= 1.03kJ / kgK, k= 1.67) at 105 k/Paa, k/P aa, 27°C and delivers deliver s it at 630 kPaa: ∆P = 0, ∆K= 0. Find the work if the process is isentropic? a. -1664kJ/min a

b. -1774 kJ/min

formula: W SF = Q - ∆H

c. -1884 kJ/min

m=p1V1 / RT1

d. -1994 kJ/min

T2= T1(p2 /p1)(k-1)/k

76. A carnot c arnot power cycle operates oper ates on o n 2 lb of o f air between be tween the t he limits lim its of 71°F and 500°F. The pressure at the beginning of isothermal expansion is 400 psia and at the end of isothermal expansion is 185psig. Determine the volume at the end of isothermal compression. a.7.849 ft 3 a

b. 7.850 ft 3

c. 7.851 ft3

d. 7852 ft 3

formula: V= mRT/ P P 3= P2[T3 / T2]

77. During a polytropic process, 10 lb of an ideal gas, whose R= 40ft.lb/lb.R and c p = 0.25Btu/lb.R, 0.25B tu/lb.R, change c hanges s state fro 20psia 2 0psia and an d 40°F to 120 psia and 340°F. Determine Deter mine n? a. 1.234 d

b. 1.345

c. 1.456

formula: [ p2 /p1 ]n-1 / n = T2 / T1

d. 1.356

78. A perfect gas has a value of R= 319.2 J/ kf.K and k= 1.26. If 120 kJ are added to 2.27 kf\g of this gas at constant pressure when the initial temp is 32.2°C? Find T 2. a. 339.4 K a

b. 449.4 K

c. 559.4K

formula: cp = kR/ k-1

d. 669.4K

Q= mc p(T2-T1)

79. A certain gas, with c p= 0.529Btu/ 0.52 9Btu/ lb. lb . °R and R = 96.2ft.lb 96 .2ft.lb/lb. /lb. °R, expand expan d s from 5 cu ft and 80°F to 15 cu ft f t while the pressure remains con stant at 15.5psia. Compute for T 2. a.15 a. 1520 20° °R b

b. 1620 16 20° °R

c. 1720 17 20° °R

d. 1820 18 20° °R

formula: T2= T1 V2 / V1

80. A System has ha s a temperature temperat ure of 250°F. Convert t his Value to °R? a. 740 74 0°R d

b.730 .7 30° °R

c. 720° 72 0°R

d. 710° 71 0°R

form fo rmul ula: a: °R= °F + 460 46 0

81) Steam with a specific volume of 0.09596 m³/kg undergoes a constant pressure process at 1.70 MPa until the specific volume becomes 0.13796 m³/kg. What are (a) the final temperature, (b) �u, (c) W, (d) �s, and (e) Q? a) 265.4°C, 430.7kJ/kg, 71.4kJ/kg, 1.0327kJ/(kg)(K) , 502.1 kJ/kg b) 204.2°C, -703.2 kJ/kg, -84.15 kJ/kg, -1.7505 kJ /(kg)(K), -787.4 kJ/kg c) 304.2°C, -803.2 kJ/kg, -89.15 kJ/kg, -2.7505 kJ /(kg)(K), -987.4 kJ/kg d) 279.4°C, 439.7kJ/kg, 79.4kJ/kg, 3.0327kJ/(kg)(K) , 602.1 kJ/kg Ans. (a) 82) Steam with an enthalpy of 2843.5 kJ/kg undergoes a constant pressure process at 0.9 MPa until the enthalpy becomes 2056.1 kJ/kg. What are (a) the initial temperature or quality, (b) �u, (c) W, (d) �s, and (e) Q? a) 265.4°C, 430.7kJ/kg, 71.4kJ/kg, 1.0327kJ/(kg)(K) , 502.1 kJ/kg b) 204.2°C, -703.2 kJ/kg, -84.15 kJ/kg, -1.7505 kJ /(kg)(K), -787.4 kJ/kg c) 304.2°C, -803.2 kJ/kg, -89.15 kJ/kg, -2.7505 kJ /(kg)(K), -987.4 kJ/kg d) 279.4°C, 439.7kJ/kg, 79.4kJ/kg, 3.0327kJ/(kg)(K) , 602.1 kJ/kg Ans. (b) Formula of #1 and #2: �u = u2 – u1, W = p(v2-v1), �s = s2-s1, Q = h2 – h1

83) At throttling calorimeter receives steam from a boiler drum at 0.11 MPa and is superheated by 10 degrees. If the boiler drum pressure is 1.55 MPa, what is the quality of the steam generated by the boiler? a) b) c) d)

95.20% 70.10% 65.60% 95.56%

Ans. (a) Formula: h1 = hf1 + x1hfg1 84) A steam calorimeter receives steam from a pipe p ipe at 0.1 MPa and 20° 20 °SH. For a pipe steam pressure of 2 MPa, what is the quality of the steam? a) b) c) d)

95.56% 70.10% 95.20% 85.10%

Ans. (a) Formula: h1 = hf1 + x1hfg1

85) A 1-kg steam-water mixture at 1.0 MPa is contained in an inflexible tank. Heat is added until the pressure rises to 3.5 MPa MP a and the temperature to 400°. Determine the heat added. a) b) c) d)

1378.7 kJ 1348.5 kJ 1278,7 kJ 1246,5 kJ

Ans. (a) Formula: Q = (h2 – p2v2) – (h1 – p1v1) 86) Water vapor at 100 KPa and 150°C is compressed isothermally until half the vapor has condensed. How much work must be performed on the steam in this compression process per kilogram? a) -1384.7 kJ b) 1384.7 kJ c) -2384.7 kJ

d) 2384.7 kJ Ans. (a) 87) Wet steam at 1 MPa flowing through a pipe is throttled to a pressure of 0.1 MPa. If the throttling temperature is 110°C, What is the qu ality of the steam in the pipe? a) b) c) d)

96% 86% 76% 66%

Ans. (a) 88) Steam is throttled to 0.1 MPa with 20 degrees of superheat. (a) What is the quality of throttled steam if its pressure is 0.75 MPa (b) What is the enthalpy of the process? a) b) c) d)

97.6%, 2713 kJ/kg -97.6%, 2713 kJ/kg 87.6%, 3713 kJ/kg -87.6%, 3713 kJ/kg

Ans. (a) 89) The pressure gauge on a 2000 m³ tank of oxygen gas reads 600kPa. How much volumes will the oxygen occupied at pressure of the outside air 100kPa? a) 14026.5 m³ b) 15026.5 m³ c) 13026.5 m³ d) 16026.5 m³ Ans. (a)Formula: P1V1/T1 = P2V2/T2 90) Assuming compression is according to the Law PV = C, Calculate the initial volume of the gas at a pressure of 2 bars w/c will occupy a volume of 6m³ when it is compressed to a pressure of 42 Bars. a) b) c) d)

130m³ 136m³ 120m³ 126m³

Ans. (d) Formula: P1V1/T1 = P2V2/T2

91) A Gas tank registers 1000kPa. After some gas has been used, the gauge registers 500kPa. What percent of the gas remains in the tank? a) b) c) d)

64.40% 74.60% 58.40% 54.60%

Ans. (d) Formula: Pabs = Patm + Pgage & % = P2/P1 * 100% 92) The volume of a gas under standard atmospheric pressure & 76cmHg is 200m³. What is the volume when pressure is 80cmHg if the temperature is unchanged? a) b) c) d)

180 170 160 190

in³ in³ in³ in³

Ans. (d) Formula: P2V2 = P1V1

93) While swimming at depth of 120m in a fresh water lake, A fish emits an air bubbles of volume 2.0mm³ atmospheric pressure is 100kPa. What is the pressure of the bubble? a) b) c) d)

217.7kPa 317.7kPa 417.7kPa 517.7kPa

Ans. (a) Formula: P = δh 94) How many joules of work is the equivalent of 15000 cal of heat? a) b) c) d)

62850 joules 3579.95 joules 14995.81 joules 15004.19 joules

Ans. (a) Formula: J = Work/Heat J = mechanical equivalent of heat whose value is 4.19 joules/calorie

95) Two thick slices of bread, when completely oxidized by the body, can supply 200,000 cal of heat. How much work is this equivalent to? a) b) c) d)

4,190,000 joules 8,390,000 joules 839,000 joules 419 000 joules

Ans. (d) Formula: J = Work/Heat J = mechanical equivalent of heat whose value is 4.19 joules/calorie 96) 3 horsepower (hp) = _____________watts? a) b) c) d)

1492 watts 2238 watts 746 watts 2238 kilowatts

Ans. (b) Formula: 1hp = 746 watts 97) How many Newton’s (N) in 900,000 dynes? a) b) c) d)

8 Newton’s 9 Newton’s 7 Newton’s 6 Newton’s

Ans. (b) Formula: 1 Newton (N) = 100,000dynes 98) Calculate the power output in horsepower of an 80-kg man that climbs a flight of stairs 3.8 m high in 4.0 s. a) b) c) d)

744.8 hp 0.998 hp 746 hp 1.998 hp

Ans. (b) Formula: Power = Fd/t = mgh/t F = W = mg d=h

99) How many calories of heat will be needed to raise the temperature of 200 g of iron from fr om 27° 27 °C to t o 80° 80 °C? (c = 0.1 0 .11 1 cal c al/g. /g. °C) a) b) c) d)

1.16kcal 2166cal 3.16kcal 4166cal

Ans. (a) Formula: H = mc �T 100) 100g 1 00g of iron ir on was heated h eated to t o 100°C and mixed mixe d wit h 22g of water at 40° 4 0°C. The final fin al temperature of the mixture was 60° 6 0°C. Show that the heat given off by the iron equals the heat absorbed by the water. a) b) c) d)

440 540 340 640

cal cal cal cal

Ans. (a) Formula: H (given off by iron) = H (absorbed by water), mc�T(iron) = mc�T(water)