ࡱ> #` Lbjbj5G5G N[W-W-<x$x$x$$4>4>4>8l>$>$#u(?p?(???CuD\D0`tbtbtbtbtbtbt$wh+zBt9x$EuC"CEEt??t(9G9G9GE?x$?`t9GE`t9G9Go"\x$s?? ͪ@`4>Es:,t4t<#us:mzFmztsmzx$s4EE9GEEEEEttF^EEE#uEEEE$$$=$$$=$$$ HYPERLINK "../../Instructor_Resources/Instructor_Guides/07_Instructor_Guides/Tutorial_07_Guide.doc" \o "Click here to view the instructor's guide"Tutorial 7: Name Section Work and energy Energy is never created nor destroyed; it just transforms from one kind to another, and from one object to another. This tutorial introduces you to energy conservation and its connection to the concept of work. HYPERLINK "../../Instructor_Resources/Instructor_Guides/07_Instructor_Guides/Tutorial_07_Guide.doc" \l "i" \o "This section combines talk about common sense and physics ideas of energy."Introduction to work, kinetic energy, and potential energy Here are some basic definitions, phrased informally: Kinetic energy = The energy something has because of its motion. The heavier or faster something is, the more kinetic energy it has. Gravitational potential energy = The energy stored in an object because its been lifted. The energy is potential because it has the potential to turn into kinetic energyfor instance, if the object gets dropped. The heavier or higher an object is, the more potential energy is stored up. A child pushes a loaded wagon up a hill, starting slowly but gradually getting faster and faster. Is the wagon gaining kinetic energy, gravitational potential energy, both, or neither? Explain. Suppose the wagon gains a total of 50 joules of energy. (A joule, like a calorie, is a unit of energy.) According to energy conservation, energy is never created nor destroyed. But the wagon just gained 50 joules! Does this scenario contradict conservation of energy? Explain why or why not. When you say something like the jogger just burned 100 calories of energy, what does that mean? Where exactly do those 100 calories come from? In other words, what form of energy is depleted by 100 calories? Hint: This is as much a biology or chemistry question as it is a physics question. Roughly speaking, work is the mechanical energythe kinetic and potential energygiven to an object by exerting a force on it. How much work did the child do on the wagon? HYPERLINK "../../Instructor_Resources/Instructor_Guides/07_Instructor_Guides/Tutorial_07_Guide.doc" \l "ii" \o "This section introduces the definition of work and applies that definition to simple situations."Lifting a book In this problem, youll use the formal definition of work to figure out some stuff. Work is done when a force F acts on the object over a distance "x. When the force points in the same direction that the object moves, the work is given by W = F"x. (In lecture, you ll deal with  misaligned forces and displacements.) A student holds a book of mass m in her hand and raises the book vertically at constant speed. Sketch a free-body diagram for the book. As the book rises at steady speed, is the force exerted by the student on the book greater than, less than, or equal to mg? Explain briefly. Suppose the student does 25 joules of work lifting the book. Does the book lifted at constant speed gain potential energy, kinetic energy, or both? Explain. Is the potential energy gained by the book greater than, less than, or equal to 25 joules? Explain. Now well repeat the reasoning of part B in terms of symbols rather than numbers. Use the definition of work to determine the amount of work the student does in raising the book through a height h. Express your answer in terms of m, g, and h. So, how much potential energy did the book gain, in terms of m, g, and h? In this class or a previous class, you may have seen the equation U = mgh for gravitational potential energy. For people who already knew that formula, whats the point of parts B and C above? ( HYPERLINK "../../Instructor_Resources/Instructor_Guides/07_Instructor_Guides/Tutorial_07_Guide.doc" \l "checkpoint1" \o "There's not much to do here besides check the questions they've just completed."Consult an instructor before you proceed.  HYPERLINK "../../Instructor_Resources/Instructor_Guides/07_Instructor_Guides/Tutorial_07_Guide.doc" \l "iii" \o "This section discusses differences between the physics and commonsense definitions of work." Pushing on a wall In this section well clarify the meaning of work. A student pushes hard enough on a wall that she breaks a sweat. The wall, however, does not move; and you can neglect the tiny amount it compresses. Does the student do any work on the wall? Answer using: your intuition. the physics definition of work. Apparently, some reconciliation is needed. Well lead you through it. In this scenario, does the student give the wall any kinetic or potential energy? Does the student expend energy, i.e., use up chemical energy stored in her body? If the energy spent by the student doesnt go into the walls mechanical energy, where does it go? Is it just gone, or is it transformed into something else? Hint: How do you feel when youve expended lots of energy? Intuitively, when you push on a wall, are you doing useful work or are you wasting energy? A student says, In everyday life, doing work means the same thing as expending energy. But in physics, work corresponds more closely to the intuitive idea of useful work, work that accomplishes something, as opposed to just wasting energy. Thats why its possible to expend energy without doing work in the physics sense. In what ways do you agree or disagree with the students analysis? HYPERLINK "../../Instructor_Resources/Instructor_Guides/07_Instructor_Guides/Tutorial_07_Guide.doc" \l "iv" \o "Here is an interesting practice problem. Click for insight on the various parts."Supplemental problem: Practice using work and energy conservation If you dont finish this problem, its OK. A similar one will appear on homework. A small, homemade rocket of mass 5.0 kg takes off from the ground and goes straight up. During the first 100 meters of its ascent, the engine exerts a 70 newton upward force on the rocket. How much work does the engine do on the rocket during those first 100 meters? Based on the given information, how much kinetic energy would you expect the rocket to have when its at a height of 100 meters? (Hint: Dont use a formula for kinetic energy. Instead, think about the relationship between work, kinetic energy, and potential energy. To keep the math less messy, approximate g as 10 m/s2.) Measurements reveal that, at height 100 meters, the rockets kinetic energy is 1800 joules, which should differ from your part B answer by 200 joules. Is energy conservation violated or is something else going on? Where are the missing 200 joules? ( Consult an instructor if you finish.     Work and energy  i j k c bc456DE{𻵮zuuujzue hr 5jJhTp>U hr 6hThr 0Jcj!hTp>Uh:jjhTUhr h34CJh34CJ$OJQJ h34>*CJ h34CJh34hTh340Jc6CJOJQJ*jh:jhTp>6CJOJQJUh:j6CJOJQJjhT6CJOJQJU' c CEƀڃjf. !D%d&dPgd34 !VJ"t"$dgd34#LL P Q R S T }~wCEƀڃjf.CEƀڃjf. ^_`awCEƀڃjf.CEƀڃjf. aF\trmr & FF$Eƀڃjf.a$CEƀڃjf.\^  ]^adų̧̡h:jhr 0JcjhTp>Uh:jjh:jU hr CJhThr 0Jc6CJ"juh:jhTp>6CJU h:j6CJjhT6CJU jhr CJ jhr CJUmHnHu hr 6hr hr 5. jklyww4CEƀڃjf.CEƀڃjf.CEƀڃjf.(wCEƀڃjf.CEƀڃjf. wrlb ^` ! & FCEƀڃjf.CEƀڃjf. w42CEƀڃjf.CEƀڃjf.CEƀڃjf.b8W[s~!!]"^"h"i"~#################LĹȰꛕꍉ~|Uhr 56OJQJhTp>jhTp>U hr CJ hr 6CJ jhr CJ hr H*hThr 0JcjhTp>Uh:jjhTUhr 6CJOJQJhr CJOJQJ hr 6hr "jh:j5CJKH OJQJU.?w4CEƀڃjf.CEƀڃjf.CEƀڃjf.wr & FCEƀڃjf.CEƀڃjf. &'(8swqhc & F  & Fh^h^CEƀڃjf.CEƀڃjf.  #!$!%!&!wuuuCEƀڃjf.CEƀڃjf.&!l"m"n"o"p"q"r"s"t"u"v"w"x"y"z"CEƀڃjf.z"v#w#x#y#z#{#|#}#~############ ^`CEƀڃjf.###SLTLLLLLLLLLLLLLLLLLLLL !$x$dN !$$dN &dP University of Maryland Physics Education Research Group, Fall 2004. 8- PAGE 3 University of Maryland Physics Education Research Group, Fall 2004. 8- PAGE 1 LELFLHLILOLPLQLRLSLTLLLLLLLLLLLLhTp>hr h:j0JCJmHnHuhr 0JCJjhr 0JCJU hr 6CJ hr CJLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL3 0&P1h/ =!"#$% zakW7{y3T( @=ԃ&\ԑ|&vmxOn@_THQ`Y$*!pRT!Ē#plrHp ,X# cdoiƱ̼m.9?=-DG_mѷODwɔC#c.f\Nйz9̜wy4yo+^'SdzD_h*1ߛǦ|o`OVJ`J( +=J( +=J( ϊVjTa'q( 3$L2^_~'-V2۽#,g$r~e'r] DE4Rw$(%ZU\q2$dnq FK)e pKiC@gYrgHRgrAV,GQES6s|=BJΑˈH֮e6a)!* % w gRs!j*z3" U􄾎 -څ;E-r9 Tޅ͡daߺ3w0fYW+r(zVYM|טTk3MbQӜF7m$yGFhi{ݾ?j;\~?%uS z*]*D&ݢ|P+bl%+=Q#X J: X)Vz@P`XVz@P`Xu"5*g,3Q)@H;aaԊĻSnVP+eCH;ebJ)+U%ZQMwJ` jEP d^+IAV$ޝXAHT "dg"w' Vw''+ Vg jEź~"9|טTfu"weNgmyD;q>loC3lJ@)IF|&vmxNQMq΅aㄉ&#+5&&| xDW 𒸒 ܻ{ʿbN!WESc_CCZkU`[.bځtKQwﻞc{pGSPB4y)E<.8JyC2M@V~ j/AUZ%*EFi0%8´Ԋς-E[B(MTtJEpZe"cգUf4?֍R*ܕ dĂ 5˺ǰnfSEAS7?xnE$|gu4 |+_"IGn&UeF3eI$|TjWv:+8D`sh=Ŗb6klv{v_u"(ФRԶu Iv-Z:j/5x}X84e zL"t*o$#J_Wszśz9'1> Comment ReferenceCJ8B8  Comment Text$CJ$L@$ Date%NYbN  Document Map&-D M OJQJ<[@r< E-mail Signature'8+8  Endnote Text(CJd$@d Envelope Address!)@ &+D/^@ OJQJF%@F Envelope Return* CJOJQJ::  Footnote Text+CJ8`@8 HTML Address,6Je@J HTML Preformatted- CJOJQJ: : Index 1.^`: : Index 2/^`: : Index 30^`: : Index 41^`:: Index 52^`:: Index 63^`:: Index 74^`:: Index 85^`:: Index 96p^p`B!B  Index Heading7 5OJQJ4/@4 List8h^h`82@8 List 29^`83@8 List 3:8^8`84@8 List 4;^`85@8 List 5<^`:0@: List Bullet = & F>6@> List Bullet 2 > & F>7@> List Bullet 3 ? & F>8@> List Bullet 4 @ & F!>9@> List Bullet 5 A & F#BD@"B List ContinueBhx^hFE@2F List Continue 2Cx^FF@BF List Continue 3D8x^8FG@RF List Continue 4Ex^FH@bF List Continue 5Fx^:1@r: List Number G & F%>:@> List Number 2 H & F'>;@> List Number 3 I & F)><@> List Number 4 J & F+>=@> List Number 5 K & F-h-h  Macro Text"L  ` @ OJQJ_HmH sH tH I@ Message HeadergM8$d%d&d'd-DM NOPQ^8`OJQJ4^@4 Normal (Web)N>@> Normal Indent O^4O@4 Note HeadingP<Z@< Plain TextQ CJOJQJ0K@0 SalutationR6@@26 Signature S^BJ@BB SubtitleT$<@&a$OJQJT,T Table of AuthoritiesU^`L#L Table of FiguresV ^` L>@rL TitleW$<@&a$5CJ KHOJQJB.B  TOA HeadingXx 5OJQJ&& TOC 1Y.. TOC 2 Z^.. TOC 3 [^.. TOC 4 \^.. TOC 5 ]^.. TOC 6 ^^.. TOC 7 _^.. TOC 8 `^.. TOC 9 a^H"H Zc Balloon TextbCJOJQJ^JaJ6U@16 T Hyperlink >*B*phFV@AF :jFollowedHyperlink >*B* ph  !"#$%&'()*+,-./0123456789:;        !!""##$$%%&&''(())**++,,--..//00112233445566778899::;  !"#$%&'()*+,-./0123456789:;>      !"#$%&'()*+,-./0123456789:TcPQRST}~^_`aF C D E  jklLEFGHIJKLMNOPQRSOPQRSTUVW~HIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~0@00h 00000 00000 00T0T0T0T0T 0000000 0000 00a 0aa0 0a0  0aa( 0 0 0 ( 0 0E 0E 0E  0aa( 0 0 0 0 0 ( 0 0 0 0  0aa0 0 0a00 00 0( 00( 000 0( 000( 00l0l( 0(00000 000 00(00L0L(00 000 0000 000000000000000 00 0 0 0 0 0 0 0 0 0 @000@000@000@000@0@0@0@0@0@0I000000000000000000000000000000000000000000000000000000000000000(cK00I00I002U0K00 ""vvLL' a&!z"#LLL !"#$()Ljb5 D XXXXXXXjqs!!_r$9C_iyuUi2$;+ 椓\b$^d`8=5rh]r$kW7{y3Ti5T"$ԃ&\T@p(  T "@ * #" B   A# *H"  # jJ"m )   c FA"Light horizontal#| ) B   "@ # B S  ? '%T _Hlt160944811 _Hlt160944812i _Hlt160944965 _Hlt160944966ii checkpoint1 _Hlt160944971 _Hlt160944972iiiivb@@@@@@ b; > :=IJ#+IJ33333bE ~=GIJ|BK}.J~ڑNÌrH4A|@Z?\Z>fG$y=^[ҞGtH2Kho |]_"&k+ *U3!]l)K,Ut.r"(5` E<.!,>` j@tKGE<Ut.j@k+k+k+k+k+k+k+k+k+~~}}||r &34Tp>:jZcT@<+4 P@PP(@P@Unknownrescherr Gz Times New Roman5Symbol3& z Arial?& Arial Black9 WebdingsCFComic Sans MS9Palatino5& zaTahoma?5 z Courier New;Wingdings?Wingdings 2"1h2FGZ 0 0!4drrr2qHP?Zc2Irescherrtomt                     Oh+'0|   , 8 D P\dltI rescherrNormaltom4Microsoft Office Word@@s]@M&@3`՜.+,D՜.+,@ hp  University of Maryland0 r I Title 8@ _PID_HLINKSA|$xoX../../Instructor_Resources/Instructor_Guides/07_Instructor_Guides/Tutorial_07_Guide.docivxp X../../Instructor_Resources/Instructor_Guides/07_Instructor_Guides/Tutorial_07_Guide.dociii} X../../Instructor_Resources/Instructor_Guides/07_Instructor_Guides/Tutorial_07_Guide.doc checkpoint1xpX../../Instructor_Resources/Instructor_Guides/07_Instructor_Guides/Tutorial_07_Guide.dociixX../../Instructor_Resources/Instructor_Guides/07_Instructor_Guides/Tutorial_07_Guide.dociX../../Instructor_Resources/Instructor_Guides/07_Instructor_Guides/Tutorial_07_Guide.docV  !"#$%&'()*+,-/012345789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrsuvwxyz{}~Root Entry Fp@`Data .1Table6zWordDocumentN[SummaryInformation(tDocumentSummaryInformation8|CompObjq  FMicrosoft Office Word Document MSWordDocWord.Document.89q