问题 填空题

如图甲所示,体积为200cm3的圆柱体A悬挂在细绳的下端静止时,细绳对物体A的拉力为F1;如图乙所示,底面积为100cm2的圆台形容器内装有适量的液体,放在水平桌面上,将圆柱体A浸没在圆筒形容器内的液体中静止时,容器内的液面升高了1.5cm,液体对容器底部的压力增加了1.8N,此时细绳对物体A的拉力为F2,且F1F2之比为3∶2,g取10N/kg。则拉力F2的大小是           N。

答案

4.8

增大的压强ΔP=ΔF/S=1.8N/100×10-4m2=180Pa

又因为P=ρgh

所以ρ液体=ΔP/gΔh=180Pa/(10N/kg×0.015m)=1.2×103kg/m3

此时的浮力 

FgV=1.2×103kg/m3×10N/kg×200×10-6m3=2.4N

根据受力分析  F1=G,F2=G-2.4

根据题意F1:F2=G:(G-2.4)=3:2

计算可得,G=7.2N  所以F2=G-2.4=4.8N

阅读理解

My students often tell me that they don’t have “enough time” to do all their schoolwork.

My reply is often a brief “You have as much time as the president.” I usually carry on a bit about there being twenty-four hours in the day for everyone, and suggest that “not enough time” is not an acceptable explanation of not getting something done.

Once in graduate school, I tried to prove to one of my professors by saying that I was working hard. His answer to me was, “That’s irrelevant (无关的). What’s important is the quality of your work.” Since then I have had time to think carefully about the “hard worker” dodge (诀窍), and I have come to some conclusions — all relevant to the problem of how much time we have.

If you analyze the matter, you can identify two parts of the problem: There is, of course, the matter of “time”, which we can think of as fixed. Then there is the problem of “work” during that time. But, as my professor suggested, it’s not how hard one works but the quality of the product that’s important.

That led me to a new idea: the quality of the work. That concept is perhaps best explained by a sign I once saw on the wall in someone’s office: “Don’t work harder. Work smarter.” There is a lot of sense in that idea.

If you can’t get more time, and few of us can, the only solution is to improve the quality of the work. That means thinking of ways to get more out of the same time than we might otherwise get. That should lead us to an analysis of our work habits. Since “work” for students usually means “homework”, the expression “work habits” should be read as “study habits”.

Then, as a smart student, you will seek to improve those skills that you use in study, chiefly reading and writing. If you learn to read better and write better, there are big benefits that pay off in all your studies.

小题1:.

From the passage, we know that the author is probably ______ .

A.a poet

B.an educator

C.a novelist

D.an engineer小题2:.

We can infer from the 2nd paragraph that we students still _____ .

A.have enough time

B.can meet the president

C.get everything done well

D.should accept the explanation小题3:.

Which of the following is TRUE according to the passage?

A.The author’s students make good use of their time to do all their homework.

B.The author tried to tell the professor that he/she (author) had done a good job.

C.You can’t improve the quality of the work if you can’t get more time.

D.You’ll try to improve your skills in reading and writing if you’re a clever student.小题4:.

What’s the passage mainly about?

A.Students don’t have enough time.

B.Don’t work harder; work smarter.

C.No one can get more time.

D.Read better and write better.

单项选择题