.

第二卷 写作（共两节，满分35分）

短文改错（共10 处错误，每个1分，满分10分）

There have some changes in sports in our school. Now we

have more than two P.E. class a week, and we have at most one

hour to exercise in every day. Students get so exciting at these

changes. More and more students take active part in the ball games,

running and jumping on the playground. Our school life is become

more colorful. Doing sports are a good way to relax and keep fit.

What’s more, a health body can help us study better or live a happier life.

小林用如图所示的滑轮组在20s的时间内把重为120N的重物匀速提升了6m，拉力所做的功为900J．求：

（1）小林所做的有用功功率；

（2）滑轮组的机械效率；

（3）拉力的大小．