This is the Multiple Choice Questions Part 4 of the Series in Power Plant Engineering as one of the Mechanical Engineering topic. In Preparation for the ME Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Exam Questions in Mechanical Engineering field, Mechanical Engineering Books, Journals and other ME References. I assume you are looking for a reviewer that will help you achieve your goal to become a License Mechanical Engineer very soon. Yes, you are in the right place to make your dream come true. Make sure to familiarize each and every questions to increase the chance of passing the Mechanical Board Examination.

#### MCQ Topic Outline included in ME Board Exam Syllabi

- MCQ in Power Plant Elements
- MCQ in Power Plant Design
- MCQ in Industrial Plant Engineering
- MCQ in Industrial Plant Design
- MCQ in Refrigeration Engineering and its Applications
- MCQ in Air Conditioning

#### Continue Practice Exam Test Questions Part 4 of the Series

โ MCQ in Power Plant Engineering Part 3 | ME Board Exam

**Choose the letter of the best answer in each questions.**

151.ย Consider a refrigerator whose 40 watts light bulb remains on continuously as a result of a malfunctionย ofย theย switch.ย Ifย theย refrigeratorย hasย aย COPย ofย 1.3ย andย the cost of electricity is 8 centsย perย kW-hr,ย determineย theย increase in the energy consumption of the refrigerator and its cost per year if the switch is not fixed.

A. P 49.59

B. P 47.59

C. P 45.59

D. P 43.59

Answer: **Option A**

Explanation:

152. A 75 hp motorย that has an efficiency of 91% is worn out and is replaced by a high-efficiency motor that has an efficiency of 95.4%. Determine the reduction in heat gain of the room due to higher efficiency under full -load conditions.

A. 2.24 kW

B. 2.44 kW

C. 2.64 kW

D. 2.84 kW

Answer: **Option B**

Explanation:

153.ย Aย householdย refrigeratorย that has a power input of 450 watts and a COP of 2.5 is to cool fiveย largeย watermelons,ย 10 kg each, to 8ยฐC. If the watermelons are initially at 20ยฐC, determine how long it will take for the refrigerator to cool them. The watermelons can be treated as water whose specific heat is 4.2 kJ/kg-K.

A. 2220 seconds

B. 2230 seconds

C. 2240 seconds

D. 2250 seconds

Answer: **Option C**

Explanation:

154.ย When a man returns to his wall-sealed house on a summer day, he finds that the house is at 32ยฐC. He returns on the air conditioner which cools the entire house to 20ยฐC in 15 minutes. If COPย isย 2.5,ย determineย theย power drawn by the air conditioner. Assume the entire mass within the house is 800 kg of air for which c_{v}ย = 0.72 kJ/kg-K, c_{p} = 1.0 kJ/kg -K.

A. 1.072 kW

B. 2.072 kW

C. 3.072 kW

D. 4.072 kW

Answer: **Option C**

Explanation:

155.ย Aย heatย sourceย atย 800 Kย lossesย 2000 kJ of heat to a sink at 500 K. Determine the entropy generated during this process.

A. 1.5 kJ/K

B. 2.5 kJ/K

C. -2.5 kJ/K

D. 4 kJ/K

Answer: **Option A**

Explanation:

156.ย Helium gas is compressed in an adiabatic compressor from an initial state of 14 psia and 50ยฐFย toย aย finalย temperatureย ofย 320ยฐFย inย aย reversibleย manner.ย Determineย theย exitย pressureย of Helium.

A. 38.5 psia

B. 40.5 psia

C. 42.5 psia

D. 44.5 psia

Answer: **Option B**

Explanation:

157.ย Airย passesย thru a nozzle with efficiency of 90%. The velocity of air at the exit is 600 m/s. Find the actual velocity atย the exit.

A. 382 m/s

B. 540 m/s

C. 458 m/s

D. 568 m/s

Answer: **Option D**

Explanation:

158.ย A 50 kg block of iron casting at 500 K is thrown into a large lake that is at a temperature of 285ย K.ย Theย ironย blockย eventuallyย reachesย thermalย equilibriumย withย theย lakeย water.ย Assuming averageย specific heat of 0.45 kJ/kg -K for the iron, determine the entropy generated during this process.

A. -12.65 kJ/K

B. 16.97 kJ/K

C. 4.32 kJ/K

D. 6.32 kJ/K

Answer: **Option C**

Explanation:

159.ย Aย windmillย withย aย 12ย mย diameterย rotorย isย toย beย installed at a location where the wind is blowingย atย anย averageย velocityย ofย 10 m/s.ย Usingย standardย conditionย ofย airย (1 atm,ย 25ยฐC), determineย the maximumย power that can be generated by the windmill.

A. 68 kW

B. 70 kW

C. 72 kW

D. 74 kW

Answer: **Option B**

Explanation:

160.ย Consider a large furnace that can supply heat at a temperature of 2000ยฐR at a steady rate ofย 3000ย Btu/s.ย Determineย theย energyย ofย thisย energy.ย Assumeย anย environmentย temperatureย of 77ยฐF.

A. 2305.19 kW

B. 2315.19 kW

C. 2325.19 kW

D. 2335.19 kW

Answer: **Option B**

Explanation:

161. A heat engine receives heat from a source at 1200 K at a rate of 500 kJ/s and rejects the wasteย heatย toย aย mediumย atย 300ย K.ย Theย powerย outputย of the engine is 180 kW. Determine the irreversibility rate for this process.

A. 190 kW

B. 195 kW

C. 200 kW

D. 205 kW

Answer: **Option B**

Explanation:

162.ย A dealer advertises that he has just received a shipment of electric resistance heaters for residential buildings that have an efficiency of 100 percent. Assuming an indoor temperature of 21ยฐC and outdoorย temperatureย of 10ยฐC, determineย the second lawย efficiency of these heaters.

A. 8.74%

B. 6.74%

C. 3.74%

D. 4.74%

Answer: **Option C**

Explanation:

163. A thermal power plant has a heat rate of 11,363 Btu/kW-hr. Find the thermal efficiency of the plant.

A. 34%

B. 24%

C. 26%

D. 30%

Answer: **Option D**

Explanation:

164.ย A rigid tank contains 2 kmol of N_{2} and 6 kmol of CO_{2} gases at 300 K and 115ย MPa. Find the tank volume using the ideal gas equation.

A. 7.33 m^{3}

B. 5.33 m^{3}

C. 3.33 m^{3}

D. 1.33 m^{3}

Answer: **Option D**

Explanation:

165.ย Aย sphericalย balloonย withย aย diameterย ofย 6ย mย isย filledย withย heliumย atย 20ยฐCย andย 200ย kPa. Determine the mole number.

A. 9.28 kmol

B. 10.28 kmol

C. 11.28 kmol

D. 13.28 kmol

Answer: **Option A**

Explanation:

166. The air in an automobile tire with a volume of 0.53 ft^{3} is at 90ยฐF and 20 psig. Determine the amountย ofย airย that must be added to raise the pressure to the recommended value of 30 psig. Assumeย theย atmosphericย pressureย toย beย 14.7ย psiaย andย theย temperatureย andย theย volumeย to remain constant.

A. 0.026 lb

B. 0.046ย lb

C. 0.066 lb

D. 0.086 lb

Answer: **Option A**

Explanation:

167.ย A rigid tankย contains 20 lb_{m}ย of air at 20 psia and 70ยฐF. More air is added to the tank until theย pressureย andย temperatureย rise to 35 psia and 90ยฐF, respectively. Determine the amount of air added to the tank.

A. 11.73 lb

B. 13.73 lb

C. 15.73 lb

D. 17.73 lb

Answer: **Option B**

Explanation:

168.ย A rigid tank contains 5 kg of an ideal gas at 4 atm and 40ยฐC. Now a valve is opened, and half of mass of the gas is allowed to escape. If the final pressure in the tank is 1.5 atm, the final temperatureย in the tank is?

A. -38ยฐC

B. -30ยฐC

C. 40ยฐC

D. 53ยฐC

Answer: **Option A**

Explanation:

169.ย Theย pressureย ofย anย automobile tire is measured to be 200ย kPa (gage) before the trip end 220ย kPa (gage)ย afterย theย tripย atย aย locationย whereย theย atmosphericย pressureย isย 90 kPa.ย Ifย the temperatureย of the air in the tire before the trip is 25ยฐC, the air temperature after the trip is?

A. 45.6ยฐC

B. 54.8ยฐC

C. 27.5ยฐC

D. 26.7ยฐC

Answer: **Option A**

Explanation:

170.ย Waterย isย boilingย atย 1 atmย pressureย inย aย stainlessย steelย panย onย anย electricย range.ย Itย is observed that 2 kg of liquid water evaporates in 30 min. The rate of heat transfer to the water is?

A. 2.07 kW

B. 0.47 kW

C. 2.51 kW

D. 3.12 kW

Answer: **Option C**

Explanation:

171.ย Considerย aย personย standingย inย aย breezyย roomย atย 20ยฐC.ย Determineย theย totalย rateย ofย heat transferย fromย thisย personย ifย theย exposedย surfaceย areaย andย theย averageย outerย surface temperatureย ofย the person are 1.6 m^{2} and 29ยฐC, respectively, and the convection heat transfer coefficient is 6 W/m^{2} with emissivity factor of 0.95.

A. 86.40 watts

B. 81.70 watts

C. 198.1 watts

D. 168.1 watts

Answer: **Option D**

Explanation:

172.ย Water is boiler in a pan on a stove at sea level. During 10 minutes of boiling, it is observed that 200 grams of water has evaporated. Then the rate of heat transfer to the water is:

A. 0.84 kJ/min

B. 45.1 kJ/min

C. 41.8 kJ/min

D. 53.5 kJ/min

Answer: **Option B**

Explanation:

173.ย Anย aluminumย panย whoseย thermalย conductivityย isย 237ย W/m-ยฐCย hasย aย flatย bottomย whose diameterย isย 20 cm and thickness of 0.4 cm. Heat is transferredย steadily to boiling water in the panย throughย itsย bottomย at a rate of 500 watts. If the inner surface of the bottom of the pan is 105ยฐC, determineย the temperatureย of the surface of the bottomย of the pan.

A. 95.27ยฐC

B. 105.27ยฐC

C. 115.27ยฐC

D. 125.27ยฐC

Answer: **Option B**

Explanation:

174. For heat transfer purposes, a standing man can be modeled as a 30 cm diameter, 170 cm long vertical cylinder with both the top and bottom surfaces insula ted and with the side surface atย anย averageย temperatureย ofย 34ยฐC.ย Forย aย convectionย heat transfer coefficient of 15 W/m^{2} -ยฐC, determineย the rate of heat loss from this man by convection in an environmentย at 20ยฐC.

A. 316.46 watts

B. 326.46 watts

C. 336.46 watts

D. 346.46 watts

Answer: **Option C**

Explanation:

175.ย Aย 5ย cmย diameterย sphericalย ballย whoseย surfaceย isย maintained at a temperature of 70ยฐC is suspendedย inย theย middleย ofย aย roomย atย 20ยฐC.ย Ifย theย convectionย heatย transferย coefficientย isย 15 W/m^{2 }-ยฐCย andย theย emissivityย ofย theย surfaceย isย 0.8,ย determineย theย totalย heatย transferย fromย the ball.

A. 23.56 watts

B. 32.77 watts

C. 9.22 watts

D. 43.45 watts

Answer: **Option B**

Explanation:

176. A frictionless piston-cylinder device and a rigid tank contain 1.2 kmol of an ideal gas at the same temperature, pressure and volume. Now heat is transferred, and the temperature of both systemsย isย raisedย byย 15ยฐC.ย Theย amountย ofย extraย heatย thatย mustย beย suppliedย to the gas in the cylinder that is maintained at constant pressure is?

A. 0

B. 50 kJ

C. 100 kJ

D. 150 kJ

Answer: **Option D**

Explanation:

177.ย A supply of 50 kg of chicken at 6ยฐC contained in a box is to be frozen to -18ยฐC in a freezer. Determine the amount of heat that needs to be removed. The latent heat of the chicken is 247 kJ/kg, and its specific heat is 3.32 kJ/kg -ยฐC above freezing and 1.77 kJ/kg -ยฐC below freezing. The containerย boxย isย 1.5ย kg,ย andย theย specificย heatย ofย theย boxย materialย isย 1.4ย kJ/kg -ยฐC.ย Alsoย the freezing temperatureย of chicken is -2.8ยฐC.

A. 15,206.4 kJ

B. 50.4 kJ

C. 15,156 kJ

D. 1,863 kJ

Answer: **Option A**

Explanation:

178.ย Waterย isย beingย heatedย inย aย closedย pan on top of a range while being stirred by a paddle wheel.ย During the process, 30 kJ of heat is transferredย to the water, and 5 kJ of heat is lost to the surrounding air. The paddle wheel work amounts to 500 N -m. Determine the final energy of the system if its initial energy is 10 kJ.

A. 35.5 kJ

B. 40.5 kJ

C. 25.5 kJ

D. 14.5 kJ

Answer: **Option A**

Explanation:

179.ย Aย classroomย thatย normallyย containsย 40ย peopleย isย toย beย air-conditionedย withย windowย air-conditioning units of 5 kW cooling capacity. A person at rest may be assumed to dissipate heat at a rateย about 360 kJ/hr. Thereย are 10 light bulbs in the room, each with a rating of 100 watts. Theย rateย ofย heatย transferย to the classroom through the walls and the windows isย ย estimated to be 15,000ย kJ/hr.ย If the room is toย beย maintained at a constant temperature of 21ยฐC, determine the numberย of window air-conditioning units required.

A. 1 units

B. 2 units

C. 3 units

D. 4 units

Answer: **Option B**

Explanation:

180.ย A 4 m x 5 m x 6 m room is to be heated by a baseboard resistance heater. It is desired that the resistance heater be able to raise the air temperature in the room from 7 to 23ยฐC within 15 minutes.ย Assumingย noย heatย lossesย fromย theย roomย andย anย atmosphericย pressureย ofย 100ย kPa, determine the required power of the resistance heater. Assume constant specific heats at room temperature.

A. 2.34 kW

B. 1.91 kW

C. 4.56 kW

D. 6.34 kW

Answer: **Option B**

Explanation:

181.ย A student living in a 4 m x 6ย m x 6ย m dormitory room turns on her 150 watts fan before she leaves the room on a summer day, hoping that the room will be cooler when she comes back in the evening. Assuming all the doors and windows are tightly closed and disregarding any heat transferย throughย the walls and the windows, determine the temperature in the room when she comes back 10 hours later. Use specific heat values at room temperature, and assume the room to be at 100ย kPaย and 15ยฐC in the morning when she leaves.

A. 28.13ยฐC

B. 38.13ยฐC

C. 48.13ยฐC

D. 58.13ยฐC

Answer: **Option D**

Explanation:

182.ย Aย piston-cylinder device whose piston is resting on top of a set of stops initially contains 0.50ย kgย ofย heliumย gasย atย 100ย kPaย andย 25ยฐC.ย Theย massย ofย theย pistonย isย suchย thatย 500ย kPaย of pressureย isย requiredย toย raiseย it.ย Howย muchย heatย mustย beย transferred to the helium before the piston starts rising?

A. 1557.13 kJ

B. 1657.13 kJ

C. 1757.13 kJ

D. 1857.13 kJ

Answer: **Option D**

Explanation:

183. In order to cool 1 ton (1000 kg) of water at 20ยฐC in an insulated tank, a person pours 80 kg ofย iceย atย -5ยฐCย intoย theย water.ย Determineย theย finalย equilibriumย temperatureย inย theย tank.ย The meltingย temperatureย andย theย heatย ofย fusionย ofย iceย at atmospheric pressure are 0ยฐC and 333.7 kJ/kg, respectively.

A. 12.43ยฐC

B. 14.43ยฐC

C. 16.43ยฐC

D. 18.43ยฐC

Answer: **Option A**

Explanation:

184.ย Aย fanย isย poweredย byย 0.5ย hp motor and delivers air at a rate of 85 m^{3}/min. Determine the highest value for the average velocity of air mobilized by the fan. Take the density of air to be 1.18 kg/m^{3}.

A. 18.23 m/s

B. 21.12 m/s

C. 25.34 m/s

D. 32.23 m/s

Answer: **Option B**

Explanation:

185.ย Anย Ocean-Thermalย Energyย Conversionย powerย plantย generatesย 10,000ย kWย usingย aย warm surface water inlet temperature of 26ยฐC and cold deep-water temperature of 15ยฐC. On the basis ofย aย 3ยฐCย dropย inย theย temperatureย ofย theย warmย waterย andย a 3ยฐC rise in the temperature of the coldย waterย dueย toย removalย andย additionย ofย heat,ย calculateย theย powerย required in kW to pump theย cold-deepย waterย toย theย surfaceย andย throughย theย systemย heatย exchangerย ifย theย required pumping pressure increase is 12 kPa. Assume a Carnot cycle efficiency and density of cold water to be 100 kg/m^{3}.

A. 108

B. 250

C. 146

D. 160

Answer: **Option B**

Explanation:

186. A plate-type solar energyย collector with an absorbing surface covered by a glass plate is to receiveย anย incidentย radiationย ofย 800 W/m^{2}.ย Theย glassย plateย hasย aย reflectivityย ofย 0.12ย and a transmissivityย ofย 0.85.ย Theย absorbingย surfaceย hasย anย absorptivityย ofย 0.90.ย Theย areaย ofย the collector is 5 m^{2}. How much solar energy in watts is absorbed by the collector?

A. 2500

B. 2880

C. 3510

D. 3060

Answer: **Option D**

Explanation:

187. A tank contains liquid nitrogen at -190ยฐC is suspended in a vacuumย shell by three stainless steel rods of 0.80 cm in diameter and 3 meters long with a thermal conductivity of 16.3 W/m^{2} -ยฐC.ย Ifย theย ambientย airย outsideย theย vacuumย shellย isย 15ยฐC,ย calculateย theย magnitudeย ofย the conductive heat flow in watts along the support rods.

A. 0.168

B. 0.0587

C. 0.182

D. 0.176

Answer: **Option A**

Explanation:

188.ย Anย elastic sphere containing gas at 120 kPa has a diameter of 1.0 m. Heating the sphere causesย itย toย expand to a diameter of 1.3 m. During theย process the pressure is proportional to the sphere diameter. Calculate the work done by the gas in kJ.

A. 41.8

B. 50.6

C. 87.5

D. 35.4

Answer: **Option C**

Explanation:

189. An ideal gas with a molecular weight of 7.1 kg/kg mol is compressed from 600 kPa and 280 K to a final specific volume of 0.5 m^{3}/kg. During the process the pressure varies according to P = 620 + 150ฯ
ย + 95 ฯ
^{2} where p is in kPa and ฯ
in m^{3}/kg. Calculate the work of compression in kJ/kg.

A. 32.8

B. 28.7

C. 35.6

D. 33.3

Answer: **Option D**

Explanation:

190.ย Aย oneย cubicย meterย container containsย aย mixtureย ofย gasesย composedย ofย 0.02ย kg-molย of oxygenย andย 0.04ย kg-molย ofย heliumย atย aย pressureย ofย 220ย kPa.ย Whatย isย theย temperature of this ideal gas mixture in Kelvin?

A. 441

B. 350

C. 400

D. 450

Answer: **Option A**

Explanation:

191. Methyl alcohol (CH_{3}OH) is burned with 25% excess air. How much unburned oxygen in kg-mol_{oxygen}/kg-mol_{fuel }will there be in the products if the combustion is complete?

A. 0.35

B. 0.45

C. 0.37

D. 0.65

Answer: **Option C**

Explanation:

192. A 12 DC electricalย motor draws a current of 15 amps. How much work in kJ does this motor produceย over a 10-minute period of operation?

A. 108.0

B. 129.6

C. 216.0

D. 318.2

Answer: **Option A**

Explanation:

193.ย A 4 liter (2-liter per revolution atย standard pressure and temperature) spark ignition engine has a compression ratio of 8 and 2200 kJ/kg heat addition by the fluid combustion. Considering a cold air-standard Otto cycle model, how much power will the engine produce when operating at 2500 rpm?

A. 166.53 hp

B. 73.12 hp

C. 97.4 hp

D. 148 hp

Answer: **Option A**

Explanation:

194.ย A simple Rankine cycle produces 40 MW of power, 50 MW of process heated and rejects 50ย MWย ofย heatย toย theย surroundings.ย Whatย isย theย utilizationย factorย ofย thisย cogenerationย cycle neglecting the pump work?

A. 50%

B. 60%

C. 64%

D. 80%

Answer: **Option C**

Explanation:

195.ย Theย rateย ofย heatย transferย to the surroundings from a person at rest is 400 kJ/hr. Suppose that the ventilation system fails in an auditorium containing 120 people and assumingย that the energy goes into the air of volume 1500 m^{3} initially at 300 K and 101 kPa, calculate the rate in ยฐC/min of air temperatureย change.

A. 0.81

B. 0.53

C. 0.63

D. 1.0

Answer: **Option C**

Explanation:

196.ย Anย insulatedย boxย containingย heliumย gasย fallsย fromย aย balloonย 4.5ย kmย aboveย theย earthโs surface. Calculate the temperature rise in ยฐCย of the helium when box hits the ground.

A. 15.2

B. 12.6

C. 25.3

D. 14.1

Answer: **Option D**

Explanation:

197. Consider two Carnot heat engines operating in series. The first engine receives heat from theย reservoirย atย 2400ย Kย andย rejectsย the waste heat to another reservoir at temperature T. The second engine receives heat by the first one, convert some of it toย work, and rejects the rest to aย reservoirย atย 300ย K.ย Ifย thermalย efficienciesย ofย bothย enginesย areย theย same,ย determineย the temperatureย T.

A. 849 K

B. 578 K

C. 763 K

D. 978 K

Answer: **Option A**

Explanation:

198. An ideal gas mixture consists of 2 kmol of N_{2} and 6 kmol of CO_{2}. The mass fraction of CO_{2} is?

A. 0.175

B. 0.250

C. 0.825

D. 0.750

Answer: **Option C**

Explanation:

199. An ideal gas mixture consists of 2 kmol of N_{2} and 6 kmol of CO_{2}. Theย apparent gas constant of mixture is?

A. 0.208

B. 0.231

C. 0.531

D. 0.825

Answer: **Option A**

Explanation:

200.ย Aย Carnotย cycleย operatesย betweenย theย temperatureย limitsย ofย 300 Kย andย 1500 K,ย and producesย 600 kWย ofย netย power.ย Theย rateย ofย entropyย changeย ofย theย workingย fluidย duringย heat addition process is ?

A. 0

B. 0.4

C. 0.5

D. 2.0

Answer: **Option C**

Explanation:

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