dνwdm am dy tv d dt m dt m 1 re g dm 从题已知,m=m0dt 272×10-129×10×15kg =2.52×10kg 所以 =2.68×103msg t m m v t v rel + = − d d d d    + = − m t m rel v v g t m m v v f f 0 d d d 0 0 gt m m v v v f f rel −         = + 0 0 ln 从题已知, ( ) 2.52 10 kg 2.72 10 1.29 10 155 kg d d 6 6 4 0 =  =  −   = − t t m mf m 2.68 10 m/s 3 所以 vf = 