化工机械设备基础作业1答案.doc

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1、Solutionstoassignment11.FindtheforceFrequiredtojuststartthelawnroller,ofradiusRandweightW,movingupovertheledgeofheighth.(Hint:juststarttheroller=noreactionforcefromthefloor)Answer:drawthefreebodydiagram;YFy=Ny-W=QandtakemomentaboutthecenterO:工M“=FxO+WxO+N/?sin0+N(/?cos0=ONx=一N、•tan^Th

2、ereforeF=-Nx=Nytan0=Wtan02.Aladderplacedonthepsmoothhorizontalgroundisinequilibrium.IfF=60kN,l=3m,a=7r/4,DeterminethereactionforcesathingeCandpointAandB.Note:AD=lm，thedistancefromCtothepointofapplicationofforceF=lm.Answers:DrawthefreebodydiagramsTakemomentaboutpointA,tosolveFbfirst.aaa

3、/5(2/sm-)-Ff/sin--0心=20kN232forceequilibriuminy・directiontosolveforFa：FB-hFA-F=0FA=60-20=40kNIsolatethepartsBCtofindtheforcesatC:厶-弟'=o^/=20kN5X（F）=0lararaFb—sillF'—lcos——kFf—/sin—=07^/=12.4kNexB32322