EF 152 Exam 3 - Spring 2017 Page 1 Copy 515

Transcription

1 EF 152 Exam 3 - Spring 2017 Page 1 Copy 515 Instructions Do not open the exam until instructed to do so. Do not leave if there is less than 5 minutes to go in the exam. When time is called, immediately stop writing, remain seated, and pass your exam to the center aisle. Working after time is called results in an automatic deduction. Turn your equation sheets in with your exam. Guidelines Assume 3 significant figures for all given numbers unless otherwise stated Show all of your work no work, no credit Write your final answer in the box provided Include units for all answers Other: c ice=0.5 cal/(g- C) p atm=14.7psi diatomic ideal gas: C p =29.1J/(mol-K) C v =20.8 J/(mol-K)

2 EF 152 Exam 3 - Spring 2017 Page 2 Copy 515 8:10 9:40 11:10 12:40 2:10 3: A102 Chris R B102 Stefy C102 Stefy D102 Chris H E102 Chris H F102 Chris H A216 Heather B216 Heather C216 Chris R D216 Chris R E216 Stefy F216 Charlie A217 Charlie B217 Thuy C217 Charlie D217 Heather E217 Thuy F217 Thuy A218 Connor B218 Connor C218 Connor D218 Michael E218 Michael F218 Michael

3 EF 152 Exam 3 - Spring 2017 Page 3 Copy 515 Name: Section: 1. Write your name and section above. Your section is on the back of the equation sheet. Specify your EXAM ID below. Use 000 if you don t know your exam ID Digit #1 Digit #2 Digit #3 4. (2 pt) Two equal mass liquids, initially at the same temperature, are heated for the same time over the same stove. You measure the temperatures and find that one liquid has a higher temperature than the other. Which liquid has a higher specific heat? The cooler one The hotter one Both the same Not enough information 5. (2 pt) A power plant generates 800 MW of electric power and 200 MW of waste heat with 600 MW of heat added. Could this heat engine exist? Yes No, It violates the 1 st law of Thermodynamics No, heat input can t be more than heat output Not enough information 6. (2 pt) Assuming an ideal gas, in a constant pressure process if the volume increases what happens to the temperature Temperature is constant Temperature Increases Temperature Decreases Not enough information 7. (2 pt) What is the source of heat in a Diesel Engine? Spark plug igniting air/gas mixture Air/gas mixture self-ignites Combustion of an external fuel (different fluid outside of cylinder) Spark plug igniting air

4 EF 152 Exam 3 - Spring 2017 Page 4 Copy (3 pt) Refer to the heating curve above for 1 gram of an unknown substance. What is the latent heat of vaporization for the substance? 0.50 J/g 0.50 J/g C 50 J/g 50 J/g C 150 J/g 150 J/g C 9. (3 pt) Refer to the heating curve above for 1 gram of an unknown substance. What is the specific heat of the substance when it is a liquid? 0.50 J/g 0.50 J/g C 50 J/g 50 J/g C 150 J/g 150 J/g C 10. (6 pts) A 115 ft long steel girder bridge is built at a temperature of 32⁰F. On a hot summer day the steel reaches a temperature of 102⁰F The coefficient of thermal expansion for steel is 7.3 x 10-6 /⁰F. The modulus of elasticity for steel is 29x10 6 lb/in 2. Determine the change in length of the steel girder in inches. Show your work, write your answer in the boxes provided, and darken the appropriate digits.

5 EF 152 Exam 3 - Spring 2017 Page 5 Copy 515 p (Pa) 8.80x10 6 B Q H C Q C Two (2) moles of air go through the process shown. Answer the questions below (assume an ideal diatomic gas. 1.4, C p =29.1J/(mol-K) C v =20.8 J/(mol-K) ) 1.1x10 6 A 6.25x10-4 5x10-3 V (m 3 ) 11. (6pts) Determine the temperature at state A in ⁰K Show your work, write your answer in the boxes provided, and darken the appropriate digits. 12. (6pts) Determine the work from A to B in kj. Show your work, write your answer in the boxes provided, and darken the appropriate digits.

6 EF 152 Exam 3 - Spring 2017 Page 6 Copy 515 p (Pa) 8.80x10 6 B Q H C Q C Same problem as previous page Two (2) moles of air go through the process shown. Answer the questions below (assume an ideal diatomic gas. ( 1.4, C p =29.1J/(mol-K) C v =20.8 J/(mol-K) ) 1.1x10 6 A 6.25x10-4 5x10-3 V (m 3 ) 13. (6pts) If the temperature difference is 2315 K, determine the heat added from B to C in kj. Show your work, write your answer in the boxes provided, and darken the appropriate digits. 14. (6pts) Determine the work from B to C in kj. Show your work, write your answer in the boxes provided, and darken the appropriate digits.

7 EF 152 Exam 3 - Spring 2017 Page 7 Copy (14 pts) A cabin s walls have an average R-value of 12 ft 2 -h-⁰f/btu and a surface area of 320 ft 2, not including the windows. The windows have an R- value of 7 ft 2 -h-⁰f/btu and a surface area of 30 ft 2. Determine the number of BTU s lost per hour if there is a 25⁰F temperature difference between the inside and outside of the cabin. 16. (14 pts) Dr.B puts 50 grams of ice cubes at a temperature of -7⁰C into 300 grams of 60⁰C water Joules are lost to the surroundings. Determine the equilibrium temperature.

8 EF 152 Exam 3 - Spring 2017 Page 8 Copy (14 pts) In lab Prof Schleter has 3.9 grams of an ideal gas at standard temperature and pressure and he compresses it adiabatically to 1/12 its original volume. Assume the gas has a molecular weight of 29.1 grams/mole and 1.4. his work input. Determine the magnitude of 18. (14 pts) The inside of an ice making machine is -13⁰C and the outside is 28 ⁰C. The coefficient of performance is 24% of ideal. If 205 kj of heat must be extracted to make one pound of ice, what is the energy required to make 30 lbs of ice?