题干

如图所示,用沿斜面向上2N的拉力,把重为5N的物体匀速拉到高处,请画出拉力的示意图和物体重力对支点O的力臂

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答案(点此获取答案解析)

过物体重心,沿与斜面平行向上的方向画一条有向线段,用F表示,大小为2N,即为其所受拉力示意图;

过物体重心,沿竖直向下的方向画一条有向线段,用G表示,大小为5N,即为其所受重力示意图;

过支点O做重力作用线的垂线段,用L表示,即为重力对支点O的力臂.如图所示:

同类题2

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项,并在答题卡上将该项涂黑。选项中有两项为多余选项。

                                                                       Wrong Reasons for Going to College

    A college education can be priceless.____If any of these following factors had abig influence on your decision, you're probably right to second-guess yourself.

   Because all your friends are going.

    In only a few weeks' time, the whole friend group will be scattered to a half dozen different colleges in a half dozen different places. Not to go will set yourself apart.____Because someone else expects it from you.

    Perhaps you come from a family where everyone goes to college,or maybe you're the kid that everyone is proud to believe will be the first toget there.____It's become so mucha part of the air you breathe that you've never stopped to consider whether you want to go or whether you're ready to go.

    ____It's beentough to find even a summer job. You don't have an alternative plan. Everyone else is doing it (see above). You think you might as well go to school. That isthe lamest(无说服力的)of reasons tospend $ 20,000 or more in the next year.

    Because you are afraid you'll regret it if you don't go.

    Your uncle tells you that he regrets that he didn't go tocollege. Others tell you they could have gone so much further in their career if only they had a college education.  ____ So this is not a persuasive reason for you togo to college.

a. A. Because you don't want to work.

b. Friends will wonder what's wrong with you.

c. Because you don't know what else to do.

d. Everyone seems more excited than you are.

e. It seems that for years everyone has just thought that ofcourse you'll go.

f. Whatever the story is, there are always people who regretdecisions they've made.

g. But maybe in your heart you know that you are going forthe wrong reasons.