work and energy review
DESCRIPTION
bookTRANSCRIPT
-
WorkandEnergyReview
P a g e |1
WorkandEnergyReviewPartA:ForcedChoiceQuestions1.Whichofthefollowingstatementsaretrueaboutwork?Includeallthatapply.a. Workisaformofenergy.b. AWattisthestandardmetricunitofwork.c. UnitsofworkwouldbeequivalenttoaNewtontimesameter.d. Akgm2/s2wouldbeaunitofwork.e. Workisatimebasedquantity;itisdependentuponhowfastaforcedisplacesan
object.f. Supermanappliesaforceonatrucktopreventitfrommovingdownahill.Thisisan
exampleofworkbeingdone.g. Anupwardforceisappliedtoabucketasitiscarried20macrosstheyard.Thisisan
exampleofworkbeingdone.h. Aforceisappliedbyachaintoarollercoastercartocarryitupthehillofthefirst
dropoftheShockwaveride.Thisisanexampleofworkbeingdone.i. Theforceoffrictionactsuponasoftballplayerasshemakesaheadfirstdiveinto
thirdbase.Thisisanexampleofworkbeingdone.j. Aneraseristiedtoastring;apersonholdsthestringandappliesatensionforceas
theeraserismovedinacircleatconstantspeed.Thisisanexampleofworkbeingdone.
k. Aforceactsuponanobjecttopushtheobjectalongasurfaceatconstantspeed.Byitself,thisforcemustNOTbedoinganyworkupontheobject.
l. Aforceactsuponanobjectata90degreeangletothedirectionthatitismoving.Thisforceisdoingnegativeworkupontheobject.
m. AnindividualforcedoesNOTdopositiveworkuponanobjectiftheobjectismovingatconstantspeed.
n. Anobjectismovingtotheright.Aforceactsleftwarduponit.Thisforceisdoingnegativework.
o. Anonconservativeforceisdoingworkonanobject;itistheonlyforcedoingwork.Therefore,theobjectwilleithergainorlosemechanicalenergy.
2.Whichofthefollowingstatementsaretrueaboutpower?Includeallthatapply.a. Powerisatimebasedquantity.b. Powerreferstohowfastworkisdoneuponanobject.c. Powerfulpeopleorpowerfulmachinesaresimplypeopleormachineswhichalways
doalotofwork.d. Aforceisexertedonanobjecttomoveitataconstantspeed.Thepowerdelivered
bythisforceisthemagnitudeoftheforcemultipliedbythespeedoftheobject.e. ThestandardmetricunitofpoweristheWatt.f. IfpersonAandpersonBdothesamejobbutpersonBdoesitfaster,thenpersonA
doesmoreworkbutpersonBhasmorepower.
-
WorkandEnergyReview
P a g e |2
g. TheNewtonmeterisaunitofpower.h. A60kgboyrunsupa2.0meterstaircasein1.5seconds.Hispowerisapproximately
80Watt.i. A300Newtonforceisappliedtoaskiertodragherupaskihillataconstantspeed
of1.5m/s.Thepowerdeliveredbythetoeropeis450Watts.3.Considerthefollowingphysicalsituations.Foreachcase,determinetheanglebetweentheindicatedforce(inboldfacetype)andthedisplacement("theta"intheworkequation).
a.0degrees b.180degrees c.90degrees d.30degrees e.60degreesa. Arightwardappliedforceisusedtodisplaceatelevisionsettotheright.b. Theforceoffrictionactsuponarightwardmovingcartobringittoastop.c. Awaiterusesanappliedforcetobalancetheweightofatrayofplatesashecarries
thetrayacrosstheroom.d. Theforceofairresistanceactsuponaverticallyfallingskydiver.e. Theforceoffrictionactsuponabaseballplayerasheslidesintothirdbase.f. AnappliedforceisusedbyafreshmantoliftaWorldCivilizationbooktothetop
shelfofhislocker.g. Abucketofwateristiedtoastringandtensionsuppliesthecentripetalforceto
keepitmovinginacircleatconstantspeed.h. Anappliedforceactingat30degreestothehorizontalisusedtodisplaceanobject
totheright.i. Agroupoffootballplayersuseanappliedforcetopushasledacrossthegrass.j. Thetensionintheelevatorcablecausestheelevatortoriseataconstantspeed.k. Inaphysicslab,anappliedforceisexertedparalleltoaplaneinclinedat30degrees
inordertodisplaceacartuptheincline.l. Anappliedforceisexertedupwardsandrightwardsatanangleof30degreestothe
verticalinordertodisplaceanobjecttotheright.m. Achildrestsontheseatofaswingwhichissupportedbythetensioninitscables;he
swingsfromthehighestpositiontoitslowestposition.4.Considerthefollowingphysicalsituations.Identifywhethertheindicatedforce(inboldfacetype)doespositivework,negativeworkornowork.
a.PositiveWork b. Negative Work c. No WorkDescriptionofPhysicalSituation
+,,ornoWorka.Acableisattached toabucketand the force of tension is usedtopullthebucketoutofawell. _______________b.RustyNalesusesahammertoexert an applied force upon astubbornnailtodriveitintothewall. _______________
-
WorkandEnergyReview
P a g e |3
c.NeartheendoftheShockwave ride, a braking system exerts anappliedforceuponthecoastercartobringittoastop. _______________d.Theforceoffrictionactsupona baseball player as he slidesintothirdbase. _______________e.Abusyspiderhangsmotionless from a silk thread, supported bythetensioninthethread. _______________f.Inbaseball,thecatcherexertsan abrupt applied force upon theballtostopitinthecatcher'smitt. _______________g.Inaphysicslab,anappliedforce is exerted parallel to a planeinclinedat30degreesinordertodisplaceacartuptheincline. _______________h.Apendulumbobswingsfromits highest position to its lowestpositionundertheinfluenceoftheforceofgravity. _______________5.Whichofthefollowingstatementsaretrueaboutconservativeandnonconservativeforces?Includeallthatapply.a. Aforceisregardedasaconservativeforceifitdoesworkbutdoesnotremove
mechanicalenergyfromasystemofobjects.b. Aforceisregardedasanonconservativeforceifitdoesnotaddmechanicalenergy
toasystemofobjects.c. Theforceofgravityandelastic(spring)forcearebothexamplesofaconservative
forces.d. Appliedforces,airresistance,frictionforces,andtensionarecommonexamplesof
nonconservativeforces.e. Physicistsenvybiologists'abilitytoinstillorderontheworldofanimalspecies
throughtheirtaxonomicsystem.Sophysicistshavemadeahabitofidentifyingforcesasconservativeandnonconservativeforcesinordertoinstillorderontheworldofforces.
f. Ifanonconservativeforceactsuponanobject,thentheobjectwilleithergainorlosemechanicalenergy.
g. Iftheonlyforceswhichdoworkuponanobjectareconservativeforces,thentheobjectwillconserveitsmechanicalenergy.
h. Ifthesumofanobject'sKEandPEisremainingconstant,thennonconservativeforcesareNOTdoingwork.
i. IfworkisNOTdoneonanobjectbyanonconservativeforce,thentheobjectwillexperienceatransformationofenergyfromkinetictopotentialenergy(orviceversa).
j. Anobjectstartsfromanelevatedpositionwith50Jofpotentialenergyandbeginsitsfalltowardstheground.IfnonconservativeforcescanbeassumedtoNOTdowork,thenatsomepointduringthefalltheobjectwillhave20Jofpotentialenergyand30Jofkineticenergy.
-
WorkandEnergyReview
P a g e |4
6.Whichofthefollowingstatementsaretrueaboutkineticenergy?Includeallthatapply.a. Kineticenergyistheformofmechanicalenergywhichdependsuponthepositionof
anobject.b. Ifanobjectisatrest,thenitdoesnothaveanykineticenergy.c. Ifanobjectisontheground,thenitdoesnothaveanykineticenergy.d. Thekineticenergyofanobjectisdependentupontheweightandthespeedofan
object.e. Fastermovingobjectsalwayshaveagreaterkineticenergy.f. Moremassiveobjectsalwayshaveagreaterkineticenergy.g. Kineticenergyisascalarquantity.h. Anobjecthasakineticenergyof40J.Ifitsmassweretwiceasmuch,thenitskinetic
energywouldbe80J.i. Anobjecthasakineticenergyof40J.Ifitsspeedweretwiceasmuch,thenits
kineticenergywouldbe80J.j. ObjectAhasamassof1kgandaspeedof2m/s.ObjectBhasamassof2kganda
speedof1m/s.ObjectsAandBhavethesamekineticenergy.k. Anobjectcanneverhaveanegativekineticenergy.l. Afallingobjectalwaysgainskineticenergyasitfalls.m. A1kgobjectisacceleratedfromresttoaspeedof2.0m/s.Thisobjectgains4.0
Joulesofkineticenergy.n. Ifworkisdoneonanobjectbyanonconservativeforce,thentheobjectwilleither
gainorlosekineticenergy.7.Whichofthefollowingstatementsaretrueaboutpotentialenergy?Includeallthatapply.a. Movingobjectscannothavepotentialenergy.b. Potentialenergyistheenergystoredinanobjectduetoitsposition.c. Bothgravitationalandelasticpotentialenergyaredependentuponthemassofan
object.d. Thegravitationalpotentialenergyofanobjectisdependentuponthemassofthe
object.e. Ifthemassofanelevatedobjectisdoubled,thenitsgravitationalpotentialenergy
willbedoubledaswell.f. Gravitationalpotentialenergyislostasobjectsfreefalltotheground.g. Thehigherthatanobjectis,themorepotentialenergywhichitwillhave.h. TheunitofmeasurementforpotentialenergyistheJoule.i. A1kgmassataheightof1meterhasapotentialenergyof1Joule.j. A1kgobjectfallsfromaheightof10mtoaheightof6m.Thefinalpotentialenergy
oftheobjectisapproximately40J.k. Ifworkisdoneonanobjectbyanonconservativeforce,thentheobjectwilleither
gainorlosepotentialenergy.
-
WorkandEnergyReview
P a g e |5
8.Whichofthefollowingstatementsaretrueaboutmechanicalenergy?Includeallthatapply.a. Thetotalamountofmechanicalenergyofanobjectisthesumofitspotential
energyandthekineticenergy.b. Heatisaformofmechanicalenergy.c. Themechanicalenergyofanobjectisalwaysconserved.d. Whennonconservativeforcesdowork,energyistransformedfromkineticto
potential(orviceversa),butthetotalmechanicalenergyisconserved.e. Abowlingballismountedfromaceilingbywayofastrongcable.Itisdrawnback
andreleased,allowedtoswingasapendulum.Asitswingsfromitshighestpositiontoitslowestposition,thetotalmechanicalenergyismostlyconserved.
f. Whenafrictionforcedoesworkonanobject,thetotalmechanicalenergyofthatobjectischanged.
g. Thetotalmechanicalenergyofanobjectremainsconstantiftheonlyforcesdoingworkontheobjectareconservativeforces.
h. Ifanobjectgainsmechanicalenergy,thenonecanbecertainthatanonconservativeforceisdoingwork.
9.Rankthesefourobjectsinincreasingorderofkineticenergy,beginningwiththesmallest.
ObjectA Object B Object C Object Dm=5.0kgv=4.0m/sh=2.0m
m=10.0 kgv=2.0m/sh=3.00m
m = 1.0 kgv=5.0m/sh=5.0m
m=5.0 kgv=2.0m/sh=4.0m
10.Rankthesefourobjectsinincreasingorderofpotentialenergy,beginningwiththesmallest.
ObjectA Object B Object C Object Dm=5.0kgv=4.0m/sh=2.0m
m=10.0 kgv=2.0m/sh=3.00m
m = 1.0 kgv=5.0m/sh=5.0m
m=5.0 kgv=2.0m/sh=4.0m
NOTE:Thenext15questionsapproximatethevalueofgas10m/s/s.11.A1200kgcaranda2400kgcarareliftedtothesameheightataconstantspeedinaautoservicestation.Liftingthemoremassivecarrequires____work.a.less b.the same c.twiceasmuchd.fourtimesasmuch e.more than 4 times as much 12.Anarrowisdrawnbacksothat50Joulesofpotentialenergyisstoredinthestretchedbowandstring.Whenreleased,thearrowwillhaveakineticenergyof____Joules.
-
WorkandEnergyReview
P a g e |6
a.50 b.morethan50 c. less than 5013.Achildliftsaboxupfromthefloor.Thechildthencarriestheboxwithconstantspeedtotheothersideoftheroomandputstheboxdown.Howmuchworkdoeshedoontheboxwhilewalkingacrosstheflooratconstantspeed?a.zeroJ b.more than zero Jc.moreinformationneededtodetermine14.A1000kgcarismovingat40.0km/hrwhenthedriverslamsonthebrakesandskidstoastop(withlockedbrakes)overadistanceof20.0meters.Howfarwillthecarskidwithlockedbrakesifitistravelingat120.km/hr?a.20.0m b.60.0m c. 90.0 m d. 120. m e.180.m15.Aplatformdiverweighs500N.Shestepsoffadivingboardthatiselevatedtoaheightof10metersabovethewater.Thediverwillpossess___Joulesofkineticenergywhenshehitsthewater.a.10 b.500 c.510 d. 5000 e. more than 5000.16.Aballisprojectedintotheairwith100Jofkineticenergy.Thekineticenergyistransformedintogravitationalpotentialenergyonthepathtowardsthepeakofitstrajectory.Whentheballreturnstoitsoriginalheight,itskineticenergyis____Joules.Doconsidertheeffectsofairresistancea.lessthan100 b. 100 c. more than 100d.notenoughinformationgiven17.Duringaconstructionproject,a2500Nobjectisliftedhighabovetheground.Itisreleasedandfalls10.0metersanddrivesapost0.100mintotheground.Theaverageimpactforceontheobjectis____Newtons.a.2500 b.25000 c. 250,000 d. 2,500,00018.A10Newtonobjectmovestotheleftat1m/s.Itskineticenergyisapproximately____Joules.a.0.5 b.1 c.10 d. more than 1019.LukeAutbeloestandsontheedgeofaroofthrowsaballdownward.Itstrikesthegroundwith100Jofkineticenergy.Lukenowthrowsanotheridenticalballupwardwiththesameinitialspeed,andthistoofallstotheground.Neglectingairresistance,thesecondballhitsthegroundwithakineticenergyof____J.a.lessthan100 b.100 c. 200 d. more than 200 e. noneofthese20.Anobjectatrestmayhave__________.
-
WorkandEnergyReview
P a g e |7
a.speed b.velocity c.acceleration d. energy e.allofthese21.A50kgplatformdiverhitsthewaterbelowwithakineticenergyof5000Joules.Theheight(relativetothewater)fromwhichthediverdovewasapproximately____meters.a.5 b.10 c. 50 d. 10022.Ajobisdoneslowly,andanidenticaljobisdonequickly.Bothjobsrequirethesameamountof____,butdifferentamountsof____.Pickthetwowordswhichfillintheblanksintheirrespectiveorder.a.energy,work b.power, work c. work, energy d.work,powere.power,energy f.force,work g. power, force h.noneofthese23.Whichrequiresmorework:liftinga50.0kgcrateaverticaldistanceof2.0metersorliftinga25.0kgcrateaverticaldistanceof4.0meters?a.liftingthe50kgsack b. lifting the25kgsackc.bothrequirethesameamount of work 24.A50.0kgcrateisliftedtoaheightof2.0metersinthesametimeasa25.0kgcrateisliftedtoaheightof4meters.Therateatwhichenergyisused(i.e.,power)inraisingthe50.0kgcrateis____astherateatwhichenergyisusedtoliftthe25.0kgcrate.a.twiceasmuch b. half as much c. thesame25.Using1000.Jofwork,asmallobjectisliftedfromthegroundfloortothethirdfloorofatallbuildingin20.0seconds.Whatpowerwasrequiredinthistask?a.20W b.50W c.100 W d. 1000 W e.20000WPartB:StraightforwardComputationalProblems26.Approximatetheworkrequiredlifta2.5kgobjecttoaheightof6.0meters.27.Astudentappliesaforcetoacarttopullitupaninclinedplaneatconstantspeedduringaphysicslab.Aforceof20.8Nisappliedparalleltotheinclinetolifta3.00kgloadedcarttoaheightof0.450malonganinclinewhichis0.636mlong.Determinetheworkdoneuponthecartandthesubsequentpotentialenergychangeofthecart.28.Eddy,whosemassis65kg,climbsupthe1.6meterhighstairsin1.2s.ApproximateEddy'spowerrating.29.A51.7kghikerascendsa43.2meterhighhillataconstantspeedof1.20m/s.Ifittakes384stoclimbthehill,thendeterminea. kineticenergychangeofthehiker.b. thepotentialenergychangeofthehiker.
-
WorkandEnergyReview
P a g e |8
c. theworkdoneuponthehiker.d. thepowerdeliveredbythehiker.30.An878kgcarskidstoastopacrossahorizontalsurfaceoveradistanceof45.2m.Theaverageforceactinguponthecaris7160N.Determine....a. theworkdoneuponthecar.b. theinitialkineticenergyofthecar.c. theaccelerationofthecar.d. theinitialvelocityofthecar.31.A510kgrollercoastercarstartsataheightof32.0m.Assumingnegligibleenergylossestofrictionandairresistance,determinethePE,KE,andspeedofthecaratthevariouslocations(A,B,C,D,andE)alongthetrack.
Location Height(m) PE (J) KE (J) velocity(m/s)Start 32.0 ________ ________ 0A 28.0 ________ ________ ________B 11.0 ________ ________ ________C 20.0 ________ ________ ________D 5.0 ________ ________ ________E 15.0 ________ ________ ________F 0 ________ ________ ________
32.A65.8kgskieracceleratesdownanicyhillfromanoriginalheightof521meters.Usetheworkenergytheoremtodeterminethespeedatthebottomofthehillif...a....noenergyislostorgainedduetofriction,airresistanceandothernonconservativeforces.b....1.40*105Jofenergyarelostduetoexternalforces.33.Usetheworkenergytheoremtodeterminetheforcerequiredtostopa988kgcarmovingataspeedof21.2m/sifthereisadistanceof45.7minwhichtostopit.PartC:WorkEnergyBarCharts,Analysis,andConceptualReasoning34.Considerthefollowingphysicalsituations.Identifytheforceswhichdoworkupontheindicatedobject(inboldfacetype)andcategorizethemasconservativeornonconservativeforces.Thenindicatewhetherthetotalmechanicalenergyoftheobjectchanges;ifitchanges,thenindicatewhetherthechangeisapositiveornegativechange.Finally,indicatewhetherthepotentialenergyandthekineticenergychanges;ifPEorKEchanges,thenindicatewhetherthechangeisapositiveornegativechange.
-
WorkandEnergyReview
P a g e |9
DescriptionofPhysicalSituation
Identity of ForcesWhichDoWork: ChangeinTME ChangeinPE ChangeinKE
Conserv.Non
Conserv.Yes
(+or) NoYes
(+or) NoYes
(+or) Noa.Aforceisappliedtomoveaphysicscartfromthefloortothetopofaninclinedplaneataconstantspeed.
__________________ _____ _____ _____ _____ _____ _____
b.Aphysicsstudentscurriesupaflightofstairsatconstantspeed. __________________ _____ _____ _____ _____ _____ _____
c.Inamomentofunsupervisedphun,aphysicsstudenthoistsherselfontoastaircasebanisterandacceleratesdownthebanister.Ignoreallfrictionforces.
__________________ _____ _____ _____ _____ _____ _____
d.Aballisdroppedfromrestfromonthetopofahillandfallstothegroundbelow.Ignoreairresistance.
__________________ _____ _____ _____ _____ _____ _____
e.Aballleavestopofahillwithalargehorizontalvelocity.Itfallstothegroundbelow.Ignoreairresistance.
__________________ _____ _____ _____ _____ _____ _____
f.AHotWheelscarisatrestatanelevatedpositionalonganinclinedplane;itisreleasedandrollstoapositionalongtheground.Ignoreairresistance.
__________________ _____ _____ _____ _____ _____ _____
g.AHotWheelscarisinmotionatthebottomofahillwhenithitsa
__________________ _____ _____ _____ _____ _____ _____
-
WorkandEnergyReview
P a g e |10
computerdisketteboxandskidstoastop.h.Apendulumbobswingsfromitshighestpositiontoitslowestposition. __________________ _____ _____ _____ _____ _____ _____
i.Aphysicscartisreleasedfromrestatanelevatedpositionalonganinclinedplane;itisreleasedandrollstoapositionalongtheinclineapproximately5cmfromthebottom.
__________________ _____ _____ _____ _____ _____ _____
35.Thediagramsbelowdepictaphysicalsituation.Analyzeeachsituationandconstructworkenergybarcharts.DescriptionofPhysicalSituation WorkEnergyBarCharta.AHotWheelscarstartsfromrestontopofaninclinedplaneandrollsdowntheinclinethroughaloopandalongahorizontalsurface.Ignoretheeffectoffrictionandairresistanceonthecar. b.AHotWheelscarstartsfromrestontopofaninclinedplaneandrollsdowntheinclinethroughaloopandalongahorizontalsurface.Frictionandairresistancehaveasignificanteffectonthecar.
c.Apendulumbobismountedontopofalabpoleanddrawnbacktoastringwhichittiedbetweentwootherpoles.Thependulumbobisreleasedfromrest.Uponreachingthevertical,thestringhitsabarrierandanewpivotpointisestablishedasthe
-
WorkandEnergyReview
P a g e |11
bobcontinuesinmotionalongan upwardtrajectory.Ignoretheeffectofairresistance.d.Atrackisconstructedbystretchingagroovedandpliablematerialbetweentwolabpoles.AmetalballstartsfromrestatpointAandrollsalongthegroovetopointB.Frictionandairresistancehaveaneffectupontheball'smotion.
e.Adartisplacedinadartgunandthespringsarecompressed.Thetriggerispulledandthedartisprojectedtowardsawall.Thedartcollideswiththewallandstickstoit.Ignoretheeffectoffrictionandairresistance.
f.BenLaborinappliesaforcetopushacratefromthebottomofaninclinedplanetothetopataconstantspeed.
36.Severalphysicalsituationsaredescribedbelow.Foreachsituation,simplifytheworkenergyequationbycancelinganyzerotermsandanyenergyterms(whetherKEorPE)whichareunchanging.Explaineachtermwhichgetscanceled.Thefirstproblemisdoneasanexample.DescriptionofPhysicalSituation Simplification ofWorkEnergy
Equationa.Aballstartsfromrestontopofatallpillarandfallstothegroundbelow.Assumetheeffectofairresistanceisnegligible.
KEi+PEi+Wnc=KEf+PEf
-
WorkandEnergyReview
P a g e |12
b.Aballstartsfromrestatanelevatedpositionalonganinclinedplaneandrollstothegroundbelow.Assumethattheeffectoffrictionandairresistanceisnegligible.
KEi+PEi+Wnc=KEf+PEf
c.Aballstartsfromrestatanelevatedpositionalonganinclinedplaneandrollstothegroundbelow.Considertheeffectoffrictionandairresistance.
KEi+PEi+Wnc=KEf+PEf
d.Atrackisconstructedbystretchingagroovedandpliablematerialbetweentwolabpoles.AmetalballstartsfromrestatpointAandrollstopointB.Frictionandairresistancehaveaneffectupontheball'smotion.
KEi+PEi+Wnc=KEf+PEf
e.Apendulumbobismountedontopofalabpoleanddrawnbacktoastringwhichittiedbetweentwootherpoles.Thependulumbobisreleasedfromrest.Uponreachingthevertical,thestringhitsabarrierandanewpivotpointisestablishedasthebobcontinuesinmotionalonganupwardtrajectory.Ignoretheeffectofairresistance.
KEi+PEi+Wnc=KEf+PEf
f.AHotWheelscarstartsfromrestontopofaninclinedplaneandrollsdowntheinclinethroughaloopand
KEi+PEi+Wnc=KEf+PEf
-
WorkandEnergyReview
P a g e |13
alongahorizontalsurface.Friction and airresistancehaveasignificanteffectonthecar.g.Anunattendedhotdogwagonstartsfromrestandrollsdownahillandupasecondhill.Ignoretheeffectoffrictionandairresistance.
KEi+PEi+Wnc=KEf+PEf
h.Arollercoastercarisalreadyinmotiononthetopofthefirstdropandrollsalongthetrackoveracoupleofhills.Ignoretheeffectoffrictionandairresistance.
KEi+PEi+Wnc=KEf+PEf
i.Acrosscountryskierisinmotionontopofasmallhill.Heskisdownthehillintothevalleyandupasecondsmallerhill.Heuseshispolestopropelhimselfduringtheentiremotion.Ignoretheeffectoffrictionandairresistance.
KEi+PEi+Wnc=KEf+PEf
PartD:ComplexAnalysisandProblemSolving37.A21.3kgchildpositionshimselfonaninnertubewhichissuspendedbya7.28mlongropeattachedtoastrongtreelimb.Thechildandtubeisdrawnbackuntilitmakesa17.4degreeanglewiththevertical.Thechildisreleasedandallowedtoswingtoandfrom.Assumingnegligiblefriction,determinethechild'sspeedathislowestpointinthetrajectory.38.Abaseballplayercatchesa163grambaseballwhichismovinghorizontallyataspeedof39.8m/s.Determinetheforcewhichshemustapplytothebaseballifhermittrecoilsahorizontaldistanceof25.1cm.39.A62.9kgdownhillskierismovingwithaspeedof12.9m/sashestartshisdescentfromalevelplateauat123mheighttothegroundbelow.Theslopehasanangleof14.1degreesandacoefficientoffrictionof0.121.Theskiercoaststheentiredescentwithoutusinghispoles;uponreachingthebottomhecontinuestocoasttoastop;thecoefficientoffrictionalongthelevelsurfaceis0.623.Howfarwillhecoastalongthelevelareaatthebottomoftheslope?40.A29.1kgsledderistravelingalongalevelareawithaspeedof8.96m/swhensheapproachesagentleinclinewhichmakesanangleof12.5degreeswiththehorizontal.
-
WorkandEnergyReview
P a g e |14
Ifthecoefficientoffrictionbetweenthesledandtheinclineis0.109,thenwhatwillbeherspeedatthebottomoftheinclinedplane,located8.21mabovethetopoftheincline.41.A221gramballisthrownatanangleof17.9degreesandaspeedof36.7m/sfromthetopofa39.8mhighcliff.Determinetheimpactspeedoftheballwhenitstrikestheground.Assumenegligibleairresistance.42.ClairedeAisleshasjustcompletedhershoppingatthegroceryfoodstore.Sheaccidentallybumpsher42.5kgcart,settingitinmotionfromrestdownahillinclinedat14.9degrees.Upondescendingadistanceof9.27metersalongtheinclinedplane,thecarthitsatreestump(whichwasplacedintheparkinglotforthesolepurposeofthisproblem).A0.295kgcanoftomatosoupisimmediatelyhurledfromthemovingcartandheadstowardsWillN.Tasue'sbrandnewLexus.UponstrikingtheLexus,thetomatosoupcancreatesadentwithadepthof3.16cm.NoahFormula,whoiswatchingtheentireincidentandfixingtodosomephysics,attemptstocalculatetheaverageforcewhichtheLexusappliestothesoupcan.AssumenegligibleairresistanceandfrictionforcesandhelpNoahout.43.PeteZariaappliesa11.9Newtonforcetoa1.49kgmugofrootbeerinordertoaccelerateitfromrestoveradistanceof1.42m.Oncereleased,howfarwillthemugslidealongthecountertopifthecoefficientoffrictionis0.728?44.SuzieLovtaskihasamassof49.7kg.Sheisatrestontopofahillwithaheightof92.6mandaninclineangleof19.2degrees.Shecoastsdownthehilltothebottomandeventuallycomestoastop;sheneverusesherpolestoapplyaforce.Thecoefficientoffrictionis0.0873alongthehilland0.527alongthehorizontalsurfaceatthebottom.WhattotaldistancewillSuziecoast(includebothinclineandlevelsurface)?45.MiaKneezhirtjumpsfromasecondstorydormroom(h=7.91m)tothegroundbelow.Uponcontactwiththeground,sheallowsher62.4kgbodytocometoanabruptstopashercenterofgravityisdisplaceddownwardsadistanceof89.2cm.CalculatetheaverageupwardforceexertedbythegrounduponMia'sfragilebody.