propane is a colorless, odorless, and flammable gas found ：丙烷是一种无色，无味，易燃气体的发现

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1、SCIENCEGrade7StudentName:_______________Date:____________TeacherName:_______________Period:__________PinOakMiddleSchool232323Sarah’slabgroupistryingtodeterminetheidentityoffourunknownpowders.Belowareeachstudent’ssuggestionsabouthowtotestthepowders.1.

2、Whichstudent’ssuggestionisthesafestwaytobegin?ASarahBDavidCLenaDKesha2.Thegirlinthepictureaboveisusingalevertoliftaheavybox.Usingthelevermakesthegirl’staskeasierby–AreducingtheinputforceBreducingthebox’smassCincreasingtheamountofworkdoneDincreasingthedist

3、ancetheboxislifted233.Inwhichofthefollowingsituationsisthegreatestamountofworkdone?Apushingwithaforceof350newtonsonacarthatdoesnotmoveBpushingabox10meterswithaforceof10newtonsCpushingacart5meterswithaforceof40newtonsDpushingawagon3meterswithaforceof70newt

4、ons4.Comparethetwosituationsshownabove.InSituation2,theboxispusheduptherampinsteadofliftedstraightup,asinSituation1.Howdoesusingthissimplemachine,calledaninclinedplane,maketheworkeasier?AdecreasesamountofworkneededtolifttheboxBdecreasesamountofforceneeded

5、tolifttheboxCdecreasestheamountofmotionneededtolifttheboxDdecreasesthedistanceoverwhichtheforceisapplied5.Howdoesaninclinedplanemakeiteasierforastudenttoliftabox1.5metersfromthefloor?AbyallowingthestudenttoapplyasmallerforceoveragreaterdistanceBbyallowing

6、thestudenttoapplyagreaterforceoverasmallerdistanceCbyincreasingtheupwardforceactingontheboxDbyincreasingtheforceofgravityactingonthebox236.TheextinctionofTexasfishspecieswasmostlikelythedirectresultofchangesinnaturalspringsandriversdueto–AdeforestationBco

7、nversionofwetlandstofarmlandCintroductionofnewfishspeciesDgroundwaterpumpinganddambuildingAquarryisanopenpitfromwhichrockcanbeobtainedbydigging,cutting,orblasting.Thequarryshownbelowcutsthroughseverallayersofsedimentarylimestonerock,labeledWthroughZ.Someo

8、ftherockfromthequarryiscrushedtomakegravelofvarioussizes.Therockandgravelareusedintheconstructionofbuildingsandroads.Largedieselmachinesandtrucksremovetherockandgravelandtransportittoconstructionsites.7.Atthequarry,