From the law of conservation of momentum: Mui=mv S S Mu=mgB 2m B 2 ui 1+ ul M=m+mB x B 2mu (m4+m==B 1+S y y  x x  O O ' ui  ' ui  − S ' ui  − A B Mui m v i B B   = From the law of conservation of momentum: 2 2 1 2 c u m u Mu m v B B B + = = M = mA +mB 2 2 1 2 ( ) c u m u m m u B A B + + = ？