Sample Exam Mp

8/18/2019 Sample Exam Mp

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Sample Exam # 3

Due: 10:07pm on Sunday, November 20, 2011

Note: You will receive no credit for late submissions. To learn more, read your instructor'sGrading olicy

!S"itc# to Standard $ssignment %ie"&

Exercise 17.28

$s a ne" mec#anical engineer or (ngines )nc*, you #ave been assigned to design brass

pistons to slide inside steel cylinders* T#e engines in "#ic# t#ese pistons "ill be used "ill

operate bet"een 20*0 and 1+0*0 * $ssume t#at t#e coeicients o epansion are

constant over t#is temperature range*Part A

) t#e piston -ust its inside t#e c#amber at 20*0 , "ill t#e engines be able to run at #ig#er

temperatures. (plain*

(ssay ans"ers are limited to about +00 "ords /00 c#aracters maimum, includingspaces*

ANSWER

:My Answer:The engine will not run at higher temps because the brass

expands faster than steel as a function temp increase

Part

) t#e cylindrical pistons are 2+*000 in diameter at 20*0 , "#at s#ould be t#e minimum

diameter o t#e cylinders at t#at temperature so t#e pistons "ill operate at 1+0*0 .

(press your ans"er using ive signiicant igures

ANSWER

: 32+*0245orrect

Exercise 17.!3

$ vessel "#ose "alls are t#ermally insulated contains *00 o "ater and 0*400 o ice,all at a temperature o 0*0 * T#e outlet o a tube leading rom a boiler in "#ic# "ater is

boiling at atmosp#eric pressure is inserted into t#e "ater*

Part A

6o" many grams o steam must condense inside t#e vessel /also at atmosp#eric pressure

to raise t#e temperature o t#e system to 2*0 . 8ou can ignore t#e #eat transerred to t#econtainer*

http://session.masteringphysics.com/myct/assignment?assignmentID=1711637http://session.masteringphysics.com/myct/assignment?assignmentID=1711637


2/5

ANSWER

: 3

215orrect

Exercise 17."$ +00*0 c#un9 o an un9no"n metal, "#ic# #as been in boiling "ater or several minutes,

is uic9ly dropped into an insulating Styrooam bea9er containing 1*+0 o "ater at room

temperature /20*0 * $ter "aiting and gently stirring or +*00 minutes, you observe t#at t#e

"ater's temperature #as reac#ed a constant value o 22*0 *

Part A

$ssuming t#at t#e Styrooam absorbs a negligibly small amount o #eat and t#at no #eat

"as lost to t#e surroundings, "#at is t#e speciic #eat o t#e metal.

ANSWER

: 3

22

5orrect

Part

;#ic# is more useul or storing t#ermal energy: t#is metal or an eual "eig#t o "ater.(plain*

(ssay ans"ers are limited to about +00 "ords /00 c#aracters maimum, including

spaces*

ANSWER

:My Answer:The specific heat of water is over 13 times greater than the

unknown metal, so the water is more useful for storing

thermal energy.

Part $

;#at i t#e #eat absorbed by t#e Styrooam actually is not negligible* 6o" "ould t#e

speciic #eat you calculated in part /a be in error. ;ould it be too large, too small, or stillcorrect. (plain*

(ssay ans"ers are limited to about +00 "ords /00 c#aracters maimum, including

spaces*

ANSWER

:My Answer:Yes there would be an error. The metal would appear as if its

specific heat was lower than in reality.

Exercise 17.7!

T#e emissivity o tungsten is 0*+0* $ tungsten sp#ere "it# a radius o 1*0+ is suspended

"it#in a large evacuated enclosure "#ose "alls are at a temperature o 00*0 *

Part A

;#at po"er input is reuired to maintain t#e sp#ere at a temperature o 200*0 i #eat


3/5

conduction along t#e supports is neglected.

Ta9e t#e Steanmann constant to be +*47?10@ *

ANSWER

: 314A0

5orrect

Exercise 17.72

8ou are as9ed to design a cylindrical steel rod 40*0 long, "it# a circular cross section,

t#at "ill conduct 10*0 rom a urnace at 0*0 to a container o boiling "ater under 1

atmosp#ere*

Part A

;#at must t#e rod's diameter be.

ANSWER

: 3

*0

5orrect

Pr%&lem 17.1'1

Bor your cabin in t#e "ilderness, you decide to build a primitive rerigerator out o

Styrooam, planning to 9eep t#e interior cool "it# a bloc9 o ice t#at #as an initial mass o

2*0 * T#e bo #as dimensions o 0*+0 0*+0 0*++0 * ;ater rom melting ice

collects in t#e bottom o t#e bo* Suppose t#e ice bloc9 is at 0*00 and t#e outside

temperature is 2*0 *

Part A) t#e top o t#e empty bo is never opened and you "ant t#e interior o t#e bo to remain

at *00 or eactly one "ee9, until all t#e ice melts, "#at must be t#e t#ic9ness o t#eStyrooam.

ANSWER

: 32*70

5orrect

Exercise 18.8

$ "elder using a tan9 o volume 7*20?10@2

ills it "it# oygen /"it# a molar mass o

2*0 at a gauge pressure o *20?10+ and temperature o *7 * T#e tan9 #as a

small lea9, and in time some o t#e oygen lea9s out* Cn a day "#en t#e temperature is 22*0

, t#e gauge pressure o t#e oygen in t#e tan9 is 1*0?10+ *

Part A

Bind t#e initial mass o oygen*


4/5

ANSWER

: 3

0*75orrect

Part

Bind t#e mass o oygen t#at #as lea9ed out*ANSWER

: 3

0*110

5orrect

Pr%&lem 18.!2

$ vertical cylindrical tan9 contains 1*70 o an ideal gas under a pressure o 1*0+ at

22*0 * T#e round part o t#e tan9 #as a radius o 11*0 , and t#e gas is supporting a piston

t#at can move up and do"n in t#e cylinder "it#out riction*

Part A

;#at is t#e mass o t#is piston.

ANSWER

: 3

1

5orrect

Part

6o" tall is t#e column o gas t#at is supporting t#e piston.

ANSWER

: 31*05orrect

Pr%&lem 18.7(

Part A

Bor "#at mass o molecule or particle is t#e rms speed eual to 1*10 at a temperature

o 00 .

ANSWER

: 3

1*0?10@1

5orrect

Part

) t#e particle is an ice crystal, #o" many molecules does it contain. T#e molar mass o

"ater is 1*0 *

ANSWER

: 3*?1011

5orrect

Part $


5/5

5alculate t#e diameter o t#e particle i it is a sp#erical piece o ice*

ANSWER

: 32*77?10@4

5orrect

Exercise 18.7

$ aguar EF convertible #as an eig#t

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