I. Multiple choice questions (1 pt. each). Please clearly indicate which answer you choose, and put a cross symbol "X" into the right box in the table on the front page.

1. Water: (a) freezes at 273° F, boils at 373° F; (b) freezes at 0 K, boils at 100 K;

~ (c) freezes at 273 K, boils at 373 K; (d) freezes at 0° F, boils at 212° F;

Le.J"'~ NciiU 2. Salts are good media for heat storage because: ~ ~ 'P~ 1 (a) They have relatively low melting temperature and low latent heat of solidifying;

W <,t Lf 1 J (b) They have relatively high melting temperature and low latent heat of solidifying; 1> ct) tC l Lt - 2.> ( c) They have relatively low melting temperature and high latent heat of solidifying; Ai\ av'bouX 4~(d) They have relatively high melting temperature and high latent heat of solidifying.

L J~V\i \)e,ro. "' 3. A real heat engine has a lower efficiency than the ideal Carnot Engine, because:

(a) The design of a real engine is never perfect; .. J \. 2 (b) A r~al engine needs to be periodically serviced, and when serviced, it does not

Lt" \f" MiJ.J / deliver power; . · f

51.-~ ( c) The operation of a real power-delivering engine always involves irreversible

f Q..;\tl \ thermodynamic processes; A* 51 "'-'1\.~.,. (d) The Second Law of Thermodynamics is only an approximation . f'~ "CI 1 'lo.

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GvJ~l/, 4. The total number of nuclei (protons and neutrons) in an atomic nucleus is called the mass number and denoted as A, The number of protons is called the nuclear charge and denoted as Z. In a ~ decay, a radioactive nucleus emits an electron, so that

(a) A increases by 2, Z decreases by 4; (b) A increases by 4, Z decreases by 2;

L tJ / \/J ~ ~ , ( c) A does not change, Z decreases by 1; · ..l q n . ~ ( d) A does not change, Z increases by 1.

'fo.>J\ J, l ro.:.~&~ E l.t,\/ t\I\ • 5. The total energy released in a single act of 235U nucleus fission is approximately:

._ 1 . ( '2 , (a) 0,2 MeV; L tJ \ V'llti!IW9 (b) 200 MeV;

f o.t\ 21 Po..f 22 (c) 200,000 MeV.

6. A pumped storage power plant is: E' . :>Ca) A net consumer of electric power because it generates slightly less energy than it ."e,"\ \ uses for pumping;

· ~to>J<U\t ~~ (b) A net provider of electric power because it generates slightly more energy than it .f~t~ \l'(,.\(,W..l- uses for pumping;

p )11'1 0\ '\/ .t S tW7' ( c) Provides exactly the same amount of energy that it consumes. -<.,.. ~ ' ~s<,t.'f> f e,o,pvv l O'l f"0

of ·· - · • W<; k'-"c.vv.... CJ ' 0"'~ 'y)o,,> ento~-i_ " . ;t j)~ ~ ..t-~.l.-1 V'~ e~,c .. e~v--01 ~~ -..+

L~ , oo / . - 5o 1 tw V\CV\AJ\ ~~~ "1 ~ ~ t~ r\'t l~~f'

si~ \/\AP~ ~~~ \ · V\tw . ·;l '~ q,, coir.s v....-VV\~v ~ \N· ~w\f\f's . CoVt~t\\lt- 11

.----------------------··----··-···

7. When the speed of wind is 20 mph, the power output from a certain wind turbine is 100 kW. When the wind speed increases by a factor of2 (i.e., to 40 mph), the power (i· O {> output: p A . ~ ~ ( 20 VY' \ , )3 • 'O .- A·~ e °1 ""'r"'J

(a) Increases by a factor of 2; l i ::.: 2' l' I J 2 - 2. (b) Increases by a factor of 4; ( ~ _.. 0 \.)3 ( O \..)3 'O

1/(c) Increases by a factor of 8; _ A-~ 11 _ l · L "'*"'f _ -=: <6 /\ ~ 2 \l'\f .!!:: <6' I .

1 ,

( d) Increases by a factor of 16; - - 2. 2_ ( e) Because of the Betz Limit, it can increase no more than 59%.

8. Below, several fuels are listed in alphabetic order. Which is the one with the highest heat of combustion?

(a) Coal; c (b) Diesel fuel;

L )J .. 'W t ·il ~ L; ( c) Firewood; J ( d) Gasoline;

f n,(14('.., 4 \ , ...e ~ ( e) Hydrog~n; ·-) (f) Natural gas.

9. The largest US hydropower plant is located at: LN ~ eti'~.3 (a) Colorado River;

J 1: \ p (b) Columbia River; ~f C\l--4' / (c) Niagara Falls; ~ f. S. ( d) Mississippi River.

10. Some renewable power resources are actually "naturally converted solar power forms". Indicate the one on the list that is not:

(a) Wind power; (b) Biomass;

L 'W W uJ:-, '/ ( c) Wave power; . '~ti 2 &:!! ..,, ( d) Geothermal power; f 0 .t\ ., (e) Hydropower.

End of the MCQ part. Please read:

I th n e pro bl f th t fi II h bl em sec 10n a o ows, m eac pro em th ere 1s a b ox: My result seems to be To me, my result looks I'm afraid I have made a major reasonable, and I am somewhat suspicious - error in my calculations, but I confident all units are seems to be way too high, really don't know where correct. or way too low.

In each problem, there is a more compact version of this table. Look critically at your result, and just circle one of the three boxes:

Seems OK Seems way too high/too low Almost sure it's badly incorrect

Please write your solutions to Problems 1 - 3 below the problem statements;

II. Problems: 1. (2 pts.) The Solar Constant -- i.e., the amount of incoming solar electromagnetic

radiation per unit area, measured on the outer surface of Earth's atmosphere in a g ane perpendicular to the rays-is approximately 1350 W/m2

• The Earth radius can be taken as approximately 6,365 km. Calculate the total solar power received by Earth at the top at its atmosphere. Hints: Does solar light come to Earth from all directions, or only from one direction? What does matter- the total surface area of an illuminated sphere ( 4nR2

), or its cross section area (nR2)? Make a simple sketch, it may help, if you are not sure.

The result I have obtained:

Seems OK Seems way too high/too low Almost sure it's badly incorrect I

~ . ..

2. (2 pts.) How much carbon dioxide is released when burning one kilogram of ethanol (ethyl alcohol, C2H60)? The atomic weight ofH is 1, of C is 12, and of 0 is 16.

The result I have obtained:

Seems OK Seems way too high/too low Almost sure it's badly incorrect

3. (3 pts.) The rotor diameter of the Vestas 80 three-blade wind turbine is 80 m. Estimate how much electrical power can be generated by this turbine if the wind speed is 17 .5 mph. Express the result in the units of MW. Take the air density as 1.25 kg/m3. 1 mile= 1609 meters; 1 hour= 3600 s. For a wind speed in the 15-20 mph range the conversion efficiency of the Vestas 80 turbine is the highest, reaching about 70% of the Betz Limit efficiency (the Betz Limit efficiency is 59%.). Hint: P = Yi pAV 3

• 3 1 ~ c. ( ,,0 ~V't' x \t~5_\ p - f 'fl &o,,.) '>( 1.1 "".., . ~ s~oos )

w\~ l~ So3 MW -- = O. gQ~~ K\J

--

The result I have obtained:

Seems OK Seems way too high/too low Almost sure it's badly incorrect

If you run out of space, you may continue on the back, but make a clear sign that there is more on the back side (e.g. "PTO" in the lower right corner)