问题 选择题

如图,水平的木板B托着木块A一起在竖直平面内做匀速圆周运动,从水平位置a沿逆时针方向运动到最高点b的过程中,下列说法正确的是

A.木块A处于超重状态

B.木块A处于失重状态

C.B对A的摩擦力越来越小

D.B对A的摩擦力越来越大

答案

AC

题目分析:AB一起做匀速圆周运动,合力提供向心力,加速度即向心加速度。水平位置a沿逆时针方向运动到最高点b的过程中,加速度大小不变,方向指向圆心.在竖直方向有竖直向下的分加速度,因此AB都处于超重状态,答案A对。对A分析,加速度指向圆心,那么此过程中水平方向加速度逐渐减小,而能够提供A水平加速度的力只有B对A的摩擦力,因此B对A的摩擦力越来越小。答案C对。

填空题
单项选择题

Last year, one group of students in Taiwan did just that. They took chances-and ended up in jail. More than 20 students paid a cram school owner to help them cheat on Taiwan’s entrance exam, according to police. The students received answers to test questions through cell phones and other electronic devices. Taiwan isn’t the only place in Asia to see major cheating scandals. In both India and South Korea, college entrance exams have been stolen and sold to students.

Academic cheating has risen dramatically over the last decade. Duke University conducted a survey of 50,000 university and 18,000 high school students in America. More than 70 percent of the students admitted cheating. Just 10 years earlier, only 56 percent said they had cheated. This trend extends far beyond the U. S., too. In Asia, where students face intense pressure to excel, the cheating problem is especially pronounced. In many Asian countries, a student’s performance is measured mostly by exam scores. And admission to a top school depends on acing standardized tests. This test-driven culture makes cheating an easy way for students to get ahead in a super-competitive academic system.

But the pressure to perform well on tests isn’t the only thing turning students into cheaters. For one, new technology makes cheating easier than ever. Students now have more sophisticated options than just "cheat sheets" hidden in pencil boxes. Today’s tech-smart students use text-messaging to discreetly send each other test answers. They post questions from standardized tests on internet bulletin boards. Students in Asia, for example, have posted questions from the Test of English as a Foreign Language (TOEFL) and the Graduate Record Exam (GRE).

Deeper issues than technology and testing, however, may be leading to the rise in academic dishonesty. Both students and educators say that society offers too many negative role models. Businesspeople make millions and scientists eam intemational acclaim by cheating and lying. The case of Korean scientist Hwang Woo Suk offers one powerful example. He faked the results of his stem cell research and became a national hero. From many sectors of society, the message to students is loud and clear: Cheating is an easy way to get ahead.

Victoria Lin, a high school teacher in Taichung, says educators must begin to stress integrity as well as achievement in academics. That’s what she tries to instill in her students. "I always tell my students, ’How much is your character worth 100 points 90 points’" Jerry Chang, a student at Taiwan’s Oriental Institute of Technology, also has words of advice for classmates he sees cheating. "When you cheat on exams, you only cheat yourself," he says, "because you won’t know how much you’ve really learned.

The example of Korean scientist Hwang Woo Suk is quoted to ()

A. shift to topic from students’ cheating to academic dishonesty

B. attribute the problem of cheating to the negative examples in our society

C. compare businesspeople and scientists in cheating scandals

D. blame technology as the most important reason for cheating