d 证牛Ⅱ：F=m dt d →F.d=m 2df=mc.寸 .d(a.b)=da.b+a.db ∴.d.=d()=5d(w)=vdw →F.di=mvdw →F.d=wmvd →Ag→6=m-3mv d a b da b a db        (  ) =  +  ( ) 2 1 dv v d v v       =  → F dr = mvdv     →  = b a v v b L a F dr mvdv   2 2 2 1 2 1 → Aa→b = mvb − mva [证] dr dt dv F dr m     →  =  dt dv F m   牛Ⅱ: = mdv v   =  ( ) 2 2 1 = d v = vdv