题目

  I spent the week before my daughter's wedding running last­minute trips to the shop and the church. To save money, I __31__ flowers from several friends who had large magnolia (木兰) trees. Their __32__ flowers would make the church beautiful.   After the rehearsal(预演) dinner the night before the wedding, I felt __33__ but satisfied this would be the best wedding any bride had ever had!   The __34__ day arrived. Patsy's fiancé (未婚夫) Tim walked with me to the church to do a final __35__. When we opened the door, I was __36__. I saw all the beautiful white flowers were2008年5月我国四川省汶川地区发生了8.0级大地震，给汶川人民造成了极大的生命财产损失，同时也产生了再次威胁人民生命财产安全的堰塞湖，唐家山堰塞湖就是其中最大、最危险的一个。 ⑴截止5月31日20时，唐家山堰塞湖水位已涨至海拔733m， 当水位继续上涨至海拔741m时，水就可以从工程人员挖的引流渠 流走，从而减轻高水位对堰体的威胁。求水位从海拔733m涨至海拔741m时，水对湖底产生的压强增大了多少？ ⑵为确保引流渠的水流畅通，需清理湖中的大型漂浮物。湖中现有一漂浮物，它浸入水中的体积是0.1m3，工作人员使用如图21所示的吊车将它打捞上岸。已知漂浮物出水后，吊车将漂浮物以20cm/s的速度提高2m的过程中，绕在滑轮组上绳子的拉力F为400N。求拉力F的功率和滑轮组的机械效率？（g 取10N/kg）