问题 问答题

(1)在做《互成角度的两个共点力的合成》实验时,以下说法中正确的有______.

A.用两只弹簧秤拉橡皮筋时,应使两细绳套之间的夹角为90°,以便算出合力的大小

B.实验中,先将其中一个弹簧秤沿某一方向拉到最大量程,然后只需调节另一个弹簧秤拉力

C.用两只弹簧秤拉橡皮筋时,结点的位置必须与用一只弹簧秤拉时结点的位置重合

D.实验中,弹簧秤必须保持与木板平行

(2)如图,在《互成角度的两个共点力的合成》实验中,若先用互成锐角的两个力F1和F2将橡皮条的结点拉到位置O,然后保持读数是F2的弹簧秤的示数不变而逐渐增大β角,在此过程中,若要保持O点位置不动,则另一个弹簧秤拉力的大小F1和方向与原来相比可能发生怎样的变化______.

A.Fl一直变大,角α先变大后变小B.Fl一直变大,角α先变小后变大

C.Fl一直变小,角α先变大后变小D.Fl一直变小,角α先变小后变大.

答案

(1)A、合力是我们根据平行四边形画出来的,不是计算出来的,同时该实验对两细绳套之间的夹角没有特别要求,故A错误.

B、实验中,弹簧的读数大小适当,便于做平行四边形即可,并非要求一定达到最大量程,故B错误.

C、为了使两次实验对橡皮筋产生的作用效果相同,故用两只弹簧秤拉时结点的位置必须与用一只弹簧秤拉时结点的位置重合,故C正确.

D、读数时,弹簧秤与木板平面平行,摩擦越小,读数越准确,故D正确.

故选:CD.

(2)F1与F2的合力不变,作出力的矢量三角形,当F2大小不变,而逐渐增大β角时,F1一直变大,角α先变大后变小.故A正确、BCD错误.

故选:A.

故答案为:(1)CD;(2)A.

阅读理解

This is a great truth, one of the greatest truths.

It is a great truth because once we truly see this truth, we transcend(超越) it. Once we truly know that life is difficult---once we truly understand and accept it---then life is no longer difficult. Because once it is accepted, the fact that life is difficult no longer matters.

Most do not fully see this truth. Instead they complain about their problems and difficulties as if life should be easy. It seems to them that difficulties represent a special kind of suffering especially forced upon them or else upon their families, their class, or even their nation.

What makes life difficult is that the process of facing and solving problems is a painful one.  Problems, depending on their nature, cause us sadness, or loneliness or regret or anger or fear. These are uncomfortable feelings, often as painful as any kind of physical pain. And since life causes an endless series of problems, life is always difficult and is full of pain as well as joy.

Yet, it is in this whole process of solving problems that life has its meaning. Problems are the serious test that tells us success from failure. When we desire to encourage the growth of human spirit, we encourage the human ability to solve problems, just as in school we set problems for our children to solve. It is through the pain of meeting and working out problems that we learn. As Benjamin Franklin said, those things that hurt, instruct. It is for this reason that wise people learn not to fear but to welcome the pain of problems.

小题1:From the passage, it can be inferred that ______.               

A.everybody has problems

B.we become stronger by meeting and solving the problems of life

C.life is difficult because our problems bring us pain

D.people like to complain about their problems小题2:The writer probably used just one short sentence in the first paragraph to ______.

A.save space

B.persuade readers

C.get readers’ attention

D.make readers laugh小题3:According to the passage, we give school children difficult problems to solve in order to______.

A.teach them to fear the pain of solving the problem

B.encourage them to learn

C.help them learn to deal with pain

D.teach them how to respect from problems小题4:The main idea of Paragraph 3 is that ______.

A.most people feel life is easy

B.most people complain about how hard their lives are

C.the writer feels life is easy

D.the writer likes to complain about his problems

单项选择题