Fixed a sign error in mechanics
Fixed a sign error in mechanics

kaichogami/sympy,yukoba/sympy,moble/sympy,garvitr/sympy,Titan-C/sympy,mcdaniel67/sympy,aktech/sympy,kaichogami/sympy,toolforger/sympy,beni55/sympy,Arafatk/sympy,atreyv/sympy,ChristinaZografou/sympy,toolforger/sympy,madan96/sympy,rahuldan/sympy,vipulroxx/sympy,kevalds51/sympy,souravsingh/sympy,debugger22/sympy,jbbskinny/sympy,pbrady/sympy,iamutkarshtiwari/sympy,jaimahajan1997/sympy,cswiercz/sympy,atsao72/sympy,debugger22/sympy,pbrady/sympy,beni55/sympy,cccfran/sympy,MridulS/sympy,sunny94/temp,flacjacket/sympy,maniteja123/sympy,emon10005/sympy,dqnykamp/sympy,farhaanbukhsh/sympy,ga7g08/sympy,garvitr/sympy,Mitchkoens/sympy,oliverlee/sympy,chaffra/sympy,asm666/sympy,lidavidm/sympy,sahilshekhawat/sympy,dqnykamp/sympy,VaibhavAgarwalVA/sympy,Gadal/sympy,pbrady/sympy,shipci/sympy,Titan-C/sympy,skidzo/sympy,sunny94/temp,shikil/sympy,sampadsaha5/sympy,sahilshekhawat/sympy,yashsharan/sympy,jamesblunt/sympy,vipulroxx/sympy,sahmed95/sympy,AkademieOlympia/sympy,drufat/sympy,grevutiu-gabriel/sympy,skidzo/sympy,Shaswat27/sympy,toolforger/sympy,VaibhavAgarwalVA/sympy,wanglongqi/sympy,MechCoder/sympy,Arafatk/sympy,meghana1995/sympy,srjoglekar246/sympy,kaushik94/sympy,AunShiLord/sympy,Curious72/sympy,ga7g08/sympy,liangjiaxing/sympy,madan96/sympy,ga7g08/sympy,pandeyadarsh/sympy,liangjiaxing/sympy,amitjamadagni/sympy,atreyv/sympy,bukzor/sympy,Gadal/sympy,souravsingh/sympy,jbbskinny/sympy,abhiii5459/sympy,mafiya69/sympy,ahhda/sympy,diofant/diofant,amitjamadagni/sympy,farhaanbukhsh/sympy,iamutkarshtiwari/sympy,iamutkarshtiwari/sympy,emon10005/sympy,lidavidm/sympy,wyom/sympy,kmacinnis/sympy,atreyv/sympy,jaimahajan1997/sympy,hrashk/sympy,shikil/sympy,sampadsaha5/sympy,Titan-C/sympy,kumarkrishna/sympy,jerli/sympy,sampadsaha5/sympy,MridulS/sympy,rahuldan/sympy,Curious72/sympy,yukoba/sympy,bukzor/sympy,AunShiLord/sympy,cccfran/sympy,hrashk/sympy,wyom/sympy,ahhda/sympy,grevutiu-gabriel/sympy,Davidjohnwilson/sympy,lindsayad/sympy,meghana1995/sympy,mcdaniel67/sympy,kaichogami/sympy,Davidjohnwilson/sympy,Vishluck/sympy,maniteja123/sympy,moble/sympy,VaibhavAgarwalVA/sympy,postvakje/sympy,beni55/sympy,asm666/sympy,saurabhjn76/sympy,garvitr/sympy,oliverlee/sympy,yashsharan/sympy,grevutiu-gabriel/sympy,ahhda/sympy,jerli/sympy,saurabhjn76/sympy,shikil/sympy,Gadal/sympy,asm666/sympy,drufat/sympy,saurabhjn76/sympy,mafiya69/sympy,skidzo/sympy,lindsayad/sympy,cswiercz/sympy,farhaanbukhsh/sympy,jaimahajan1997/sympy,MechCoder/sympy,hargup/sympy,Vishluck/sympy,dqnykamp/sympy,postvakje/sympy,sahmed95/sympy,Davidjohnwilson/sympy,shipci/sympy,hargup/sympy,yukoba/sympy,MechCoder/sympy,pandeyadarsh/sympy,atsao72/sympy,atsao72/sympy,jbbskinny/sympy,jamesblunt/sympy,Mitchkoens/sympy,mcdaniel67/sympy,rahuldan/sympy,lindsayad/sympy,abhiii5459/sympy,abloomston/sympy,abhiii5459/sympy,liangjiaxing/sympy,madan96/sympy,abloomston/sympy,postvakje/sympy,kumarkrishna/sympy,jerli/sympy,wyom/sympy,ChristinaZografou/sympy,maniteja123/sympy,kmacinnis/sympy,moble/sympy,pandeyadarsh/sympy,MridulS/sympy,Arafatk/sympy,Shaswat27/sympy,Vishluck/sympy,mafiya69/sympy,jamesblunt/sympy,hargup/sympy,Designist/sympy,sahmed95/sympy,wanglongqi/sympy,hrashk/sympy,aktech/sympy,debugger22/sympy,shipci/sympy,meghana1995/sympy,Sumith1896/sympy,Sumith1896/sympy,sunny94/temp,kaushik94/sympy,drufat/sympy,cswiercz/sympy,AunShiLord/sympy,Shaswat27/sympy,lidavidm/sympy,skirpichev/omg,wanglongqi/sympy,vipulroxx/sympy,kmacinnis/sympy,chaffra/sympy,abloomston/sympy,Mitchkoens/sympy,AkademieOlympia/sympy,yashsharan/sympy,souravsingh/sympy,Sumith1896/sympy,cccfran/sympy,emon10005/sympy,Designist/sympy,oliverlee/sympy,kevalds51/sympy,ChristinaZografou/sympy,AkademieOlympia/sympy,sahilshekhawat/sympy,kaushik94/sympy,Designist/sympy,aktech/sympy,kevalds51/sympy,bukzor/sympy,kumarkrishna/sympy,Curious72/sympy,chaffra/sympy