9/16/2015 MasteringPhysics:Ch21HW

https://session.masteringphysics.com/myct/itemView?assignmentProblemID=54120376&view=print&offset=next 1/3

Coulomb'sLawTutorial

LearningGoal:

Tounderstandhowtocalculateforcesbetweenchargedparticles,particularlythedependenceonthesignofthechargesandthedistancebetweenthem.

Coulomb'slawdescribestheforcethattwochargedparticlesexertoneachother(byNewton'sthirdlaw,thosetwoforcesmustbeequalandopposite).Theforce exertedbyparticle2(withcharge )onparticle1(withcharge )isproportionaltothechargeofeachparticleandinverselyproportionaltothesquareofthedistance betweenthem:

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where and istheunitvectorpointingfromparticle2toparticle1.Theforcevectorwillbeparallelorantiparalleltothedirectionof ,paralleliftheproduct andantiparallelif theforceisattractiveifthechargesareofoppositesignandrepulsiveifthechargesareofthesamesign.

PartA

Considertwopositivelychargedparticles,oneofcharge(particle0)fixedattheorigin,andanotherofcharge(particle1)fixedontheyaxisat .Whatis

thenetforce onparticle0duetoparticle1?

Expressyouranswer(avector)usinganyorallof ,, , , , ,and .

ANSWER:

Correct

PartB

Nowaddathird,negativelycharged,particle,whosechargeis (particle2).Particle2fixedontheyaxisatposition .Whatisthenewnetforceonparticle0,fromparticle1andparticle2?

Expressyouranswer(avector)usinganyorallof , , , , , , , ,and .

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9/16/2015 MasteringPhysics:Ch21HW

https://session.masteringphysics.com/myct/itemView?assignmentProblemID=54120376&view=print&offset=next 2/3

ANSWER:

Correct

PartC

Particle0experiencesarepulsionfromparticle1andanattractiontowardparticle2.Forcertainvaluesof and,therepulsionandattractionshouldbalanceeachother,resultinginnonetforce.Forwhatratio isthere

nonetforceonparticle0?

Expressyouranswerintermsofanyorallofthefollowingvariables: , , , .

ANSWER:

Correct

PartD

Nowaddafourthchargedparticle,particle3,withpositivecharge ,fixedintheyzplaneat .Whatisthenetforce onparticle0duesolelytothischarge?

Expressyouranswer(avector)using , , , , , ,and .Includeonlytheforcecausedbyparticle3.

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9/16/2015 MasteringPhysics:Ch21HW

https://session.masteringphysics.com/myct/itemView?assignmentProblemID=54120376&view=print&offset=next 3/3

Hint1.Findthemagnitudeofforcefromparticle3

Whatisthemagnitudeoftheforceonparticle0fromparticle3,fixedat ?

Expressyouranswerusing , , , .

Hint1.Distancetoparticle3

UsethePythagoreantheoremtofindthestraightlinedistancebetweentheoriginand .

ANSWER:

Hint2.Vectorcomponents

Theforcevectorpointsfrom to .Because issymmetricallylocatedbetweentheyaxisandthezaxis,theanglebetween ,theunitvectorpointingfromparticle3toparticle0,andtheyaxisisradians.Youhavealreadycalculatedthemagnitudeofthevectorabove.Nowbreakuptheforcevectorintoitsyandzcomponents.

ANSWER:

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