Name: Applied Physics II Exam 2 Winter Multiple Choice ( 8 Points Each ):

Transcription

1 Name: Applied Physics II Exam 2 Winter Multiple Choice ( 8 Points Each ): 1. A cowboy fires a silver bullet ( specific heat c = 234 J / kg O C ) with a muzzle speed of 200 m/s into a pine wall of the saloon. Assume that all the internal energy generated by the impact remains with the bullet, i.e., all the kinetic energy goes into heating the bullet and none of the energy goes into heating the wall or changing the structure of the wall. What is the final temperature change of the bullet when it has stopped in the wall? a.) 70.2 O C b.) 63.2 O C c.) 95.1 O C d.) 85.5 O C 2. A 10 kg block of ice is at 0.0 O C. How much energy is required to turn it into 10 kg of water at 0.0 O C? ( latent heat of fusion of water L f = 3330 J / kg, latent heat of vaporization of water L v = 2.26 X 10 6 J / kg, specific heat c ice = 2090 J / kg O C, specific heat c water = 4186 J / kg O C, specific heat c steam = 2010 J / kg O C ) a.) J b.) J c.) J d.) J 3. A student is trying to decide what to wear after getting out of the shower. The surrounding temperature of the bathroom is 20 O C. The temperature of the skin of the student is 35 O C. What is the net temperature loss from the body in 10.0 minutes? ( Assume the emissivity of the skin is 0.90 and the surface area of the body s 1.50 m 2 ) a.) 7.5 X 10 4 J b.) 9.5 X 10 4 J c.) 2.5 X 10 4 J d.) 41 J

2 4. A 1.0 mole sample of an idea gas is kept at a constant temperature of 0.0 O C during an isothermal expansion from 3.0 L to 10.0 L. How much work is done by the gas during the expansion? a.) -7.5 X 10 4 J b.) +8.5 X 10 3 J c.) +2.7 X 10 3 J d.) +400 J 5. How much energy transfer by heat occurs with the surrounding during the surroundings in this expansion in Question 4? a.) -7.5 X 10 4 J b.) +8.5 X 10 3 J c.) -2.7 X 10 3 J d.) +400 J 6. If the gas in Question 4 is returned to its original volume by means of an isobaric process, how much work is done on the gas? a.) -7.5 X 10 4 J b.) +1.6 X 10 3 J c.) -1.6 X 10 3 J d.) +400 J

3 7. Determine the work done on a fluid that expands from V i to V f? P (Pa) 6 X X X 10 6 V( m 3 ) a.) -16 X 10 6 J b.) -8 X 10 6 J c.) -12 X 10 6 J d.) -32 X 10 6 J 8. A heat engine operates between two reservoirs at temperatures between 20.0 O C and O C. What is the maximum efficiency possible for this engine? a.) 100 % b.) 48.9 % c.) 24.5 % d.) 97.8 % 9. Entropy can be defined as: a.) A measure of the internal energy of a system. b.) A measure of the heat required to bring a system to rest. c.) A measure of the disorder of a system. d.) A measure of the rotational energy of the system.

4 10. During one cycle, an engine extracts 3000 J of energy from a hot reservoir and transfers 1500 J of energy to a cold reservoir. Find the thermal efficiency of the engine and the amount of work the engine does in one cycle. a.) 50 % and 1500 J b.) 25 % and 1500 J c.) 50 % and 3500 J d.) 25 % and 3500 J

5 Problem One ( 10 Points ): Heat is added to 10 kg block of ice at -10 O C to turn it into steam at +110 O C. ( latent heat of fusion L f = 3330 J / kg, latent heat of vaporization L v = 2.26 X 10 6 J / kg, specific heat c ice = 2090 J / kg O C, specific heat c water = 4186 J / kg O C, specific heat c steam = 2010 J / kg O C ) a.) (1 pts.) How much heat was added to the 10 kg sample to bring it to 0 O C? b.) (1 pts.) How much heat was to melt the 10 kg at 0 O C? J J c.) (1 pts.) How much heat was added to the 10 kg sample to bring it 0 O C to 100 O C? J d.) (1 pts.) How much heat was added to turn the 10 kg sample to stream at 100 O C? J e.) (1 pts.) How much heat was added to the 10 kg sample to bring it from 100 O C to 110 O C? J f.) (2 pts.) What is the total energy added to 10 kg During this process? J g.) (3 pts.) Draw a rough graph of the temperature of the 10 kg sample versus the heat added. ( Blank page follows to show work. Test continues after the blank page. )

6 ( This is a blank page follows to show work for problem One. Test continues after this blank page. )

7 Problem Two ( 10 Points ): A 20 square foot wall consists of 4.0 inch brick, followed by sheathing 0.25 inch thick, followed by an airspace 3.5 inches thick, followed by drywall that is 0.50 inch thick. The temperature inside the building is 20 O C and outside the building the temperature is 0 O C. ( Don't forget to add units to answers.) 4 in. 3.5 in in. 0.5 in. R brick 4 in. =4.00 ft 2. O F h R sheathing 0.25in. =0.66 ft 2. O F h R drywall 0.5in. =0.45 ft 2. O F h R airspace3.5in. =0.17 ft 2. O F h R fiber glass 3.5in. =10.90 ft2. O F h a.) (2 pts.) What is the R value for the wall constructed? b.) (3 pts.) How much heat is lost due to thermal conduction in one day? c.) (2 pts.) To reduce heat lost, the airspace is filled with fiberglass insulation 3.5 inches thick. What is the new R value for the wall constructed? d.) (3 pts.) How much heat is lost due to thermal conduction in one day after the insulation is installed? ( Blank page follows to show work. Test continues after the blank page. )

8 ( This is a blank page follows to show work for problem One. Test continues after this blank page. )

9 Extra Credit ( 10 Points ): An electrical power plant has an overall efficiency of 15%. The plant is to deliver 150 MW of electrical power to a city, and its turbine uses coal as fuel. The burning coal produces steam at 190 O C, which drives the turbine. The steam is condensed into water at 25 O C by passing through coils of a condenser that exhausts heat to a river. ( heat of combustion of coal is 7800 cal/g ) ( 1 cal = J ) a.) ( 5 pts.) Draw a diagram of the electrical power plant. b.) ( 5 pts.) How many metric tons of coal ( 1 metric ton = 1000 kg) does the plant consume each day?