如图所示，小刚在5s内将一重为540N的物体匀速向上提起1m，拉力为300N．（不计摩擦及绳重）

求：⑴小刚拉绳的功率；⑵滑轮组的机械效率．

除去下列不纯物质中的少量杂质（括号内为杂质），请填入适当的试剂

（1）Cu（Al）____     （2）Fe₂O₃（Al₂O₃）   ____

（3）NO（NO₂） ____ （4）NaCl溶液（Na₂CO₃） ____．

增加：在缺词处加一个漏字符号（∧）并在其下面写出该加的词。

删除：把多余的词用斜线（＼）划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1）每处错误及其修改均仅限一词；

2）只允许修改10处，多者（从第11处起）不计分。

    On Sunday morning, Jack was painting in the study while the phone rang. He hurried to the phone. He was his workmate, Mike. While they were chatting on the phone, but his little son knocked over painting. Jack rushed back to the study. The painting was on a mess and the baby was crying. He quickly cleared the mess, comforting the baby and then took him out. To his surprises, his wife came back from shopping ahead of the usually time. He was rather embarrassing. He told his wife that it was the cat which caused the disaster.