Expert: Jayendra Upadhye - 5/12/2006

Question
1. Which of the following takes place in the combustion chamber of a gas turbine engine?
A. Fuel oil is stored with sufficient pressure
B. Fuel oil is mixed with a proper portion of compressed air.
C. A mixture of fuel oil and compressed air is ignited.
D. Gases are cooled to a desired temperature.

2. How much heat energy is required to raise the temperature of 5 kilograms of coal from 20 degrees celsius to 220 degrees celsius?
A. 314 J
B. 6,573 J
C. 1,314,718 J
D. 4,187,000 J

3. One degree Celsius indicates the same temperature change as
A. one degree Fahrenheit
B. one kelvin
C. 5/9 degree Fahrenheit
D. 9/5 kelvin

4. A quantity of a gas has an absolute pressure of 400 kPa and an absolute temperature of 110 degrees kelvin. When the temperature of the gas is raised to 235 degrees kelvin, what is the new pressure of the gas? (Assume that there's no change in volume.)
A. 1.702 kPa
B. 3.636 kPa
C. 510 kPa
D. 854046 kPa

5. If the absolute pressure of a gas is 550.280 kPa, its gage pressure is
A. 101.325 kPa
B. 277.280 kPa
C. 448.955 kPa
D. 651.605 kPa

6. Which one of the following substances is a liquid fuel used in rocket engines?
A. Liquid oxygen
B. Ammonia
C. Potassium perchlorate
D. Codium nitrate

17. The density of water is the greatest at a temperature of
A. 0 K
B. 4 K
C. 273 K
D. 277 K

18. How much heat is required to convert 0.3 kilogram of ice at 0 degrees celsius to water at the same temperature?
A. 100,375 J
B. 167,292 J
C. 334,584 J
D. 450,759 J

Thanks soooo very much!

Answer
Hi Brittnie,
I accept your request..
1 - This is a strange question as both b and c hold true!!
In the combustion chamber of a jet engine (gas turbine), the incoming hot air (as it is compressed to about 15 atmospheres it becomes hot of its own accord) and fuel are mixed and ignited too! "ignited" once only initially. the flame "holds" or sustains itself once the engine gets going.
So both b & c hold true. Hope this is a multiple possibilities question.

2 - I have a faint feeling some one is pulling someones leg here...my dear, that would be = 5 * specific heat of coal * 200 = 1000 * specific heat of coal (in KCal /Kg)! But what is the temperature at which coal actually begins to smoulder and start its own exothermic reactions (burns at low heat)?
Specific heat of coal is one unknown variable here!!
sorry cant answer comprehensively.

3 - B

4 - p2/p1 = t2/t1 as volume is constant and we assume isothermal (slow) heat transfer to the gas.
thus p2 = (235/110)* 400 = 854.545 kpa
D should be reading 854.545 & not 854046 kPa.

5 - C
because atmospheric pressure + gauge pressure = absolute pressure, and since atmospheric pressure is roughly 100 kpa,
we get 550.280 kPa absolute pressure - 100 kpa atmospheric pressure = approx 450.280 kPa gauge pressure. hence C is our choice.
ref:- http://en.wikipedia.org/wiki/Pressure

6 - A.
This is the famed LOX fuel. (Liquid Oxygen normally used with Liquic hydrogen in cryogenic engines. The famous saturn 5 rockets used Liquid oxygen and Kerosene!!
Trust me in India they use rags soaked in liquid oxygen as dynamite!

17 - B.
At 4 degrees C, it undergoes anomalous expansion and often cracks iron pipes.

18 - the specific heat of fusion for pure water is 80,000 calories /kg.
So for 0.3 kilos of ice, one would require 80000*0.3 = 8000*3 = 24000 calories.
since 1 International Table calorie = 4.1868 J (exact)
ref:- http://en.wikipedia.org/wiki/Joule
24000 calories = 100483.2 J
Hence our choice should be A.
Hope that suffices.

Jayen