Two particles of masses  m1  and  m2  repel each other by a force  F   =    Cr2, where C is a constant and r the separation between  m1  and  m2 mass m1is fixed and m2  is released from rest from on initial separation  ri  from  m1.   Speed of  m2 when it is at extremely large distance from  m1, while moving away from  m1 is ,

U  =∫F.dr  U = ∫Cr2.dr U=-Cr applying conservation of Energy     Uinitial  +Kinitial   =    Ufinal+Kfinal   Uinitial =Ui     =  Cri    ;       Ki   =    0   m1 is at rest ; m2 is released ∴       Kf  =   12 m2V2 ,       Uf    =    0=C∞ substitute the values in conservation of Energy    ∴ 0+      Cri   =   12 m2V2 +0   ⇒     V  =    2Cm2ri 12