GOTHENBURG, Neb. (AP) – Officials say a semitrailer rammed intothe back of a recreational vehicle in western Nebraska, killing a passenger in the big rig.     The accident occurred around 4:15 a.m. Sunday, on Interstate 80 between Gothenburg and Cozad.     Authorities say the truck driven by 56-year-old Bogdan Kaszubahit the rear of the RV. The truck then hit a bridge railing. A passenger in the truck’s sleeping compartment died at the scene.  He was identified as 56-year-old Andrzej Piaszczynski (AHN’-draypuh-CHOO’-skee.)     State Trooper Ken Moody says Kaszuba was treated for minor injuries.     Moody said Monday that a 12-year-old boy in the RV was seriously injured but was expected to survive. Four other people in the RV suffered a variety of injuries.