(1)因为蜡烛是圆柱形,蜡烛对桌面的压强P======ρgh=0.8×103kg/m3×9.8N/kg×0.1m=784Pa, (2)F浮=G蜡+G铅丝,设未燃烧时蜡烛的长度为h,燃烧至与水面相平时蜡烛的长度为h′,蜡烛的体积V=sh, 未燃烧时ρ水gV排=ρ蜡gV蜡+G铅丝, ρ水g(sh)=ρ蜡g(sh)+G铅丝…①, 燃烧相平时,ρ水g=ρ蜡g+G铅丝, ρ水g(sh′)=ρ蜡g(sh′)+G铅丝…② 由①-② ρ水g(sh)-ρ水g(sh′)=ρ蜡g(sh)-ρ蜡g(sh′), 即ρ水h-ρ水h′=ρ蜡h-ρ蜡h′…③, 将h=10cm=0.1m,ρ蜡=0.8×103kg/m3,代入③解得h′=5cm=0.05m. 故答案为:784;5. |