问题 选择题

一个物体受到F1、F2、F3、F4、F5五个力的作用而处于静止状态,其中F1 =10N,F2 =10N,F1与F2互相垂直。现将F1从10N慢慢减小到5N,同时F2从10N慢慢增大到15N,且这两个力的大小改变的快慢相同,其它几个力保持不变,则此过程中,下列说法正确的是

A.物体的加速度先减小后增大

B.物体的加速度一直增加

C.物体的速度先减小后增加

D.物体将做变加速直线运动

答案

BD

题目分析:设F1竖直向上,则F1从10N慢慢减小到5N,说明向下的合外力逐渐增加到5N,说明加速度先增加。设F2水平向右,则同时F2从10N慢慢增大到15N,说明向右合外力逐渐增加5N,根据勾股定理,则合外力逐渐增加,所以A错B对。由于物体从静止开始运动,分方向的加速度使得分速度逐渐增加,所以速度逐渐增加,由于合外力方向在变,所以不可能作直线运动,所以答案为BD

点评:本题考查了曲线运动条件、分运动与合运动,并利用条件判断轨迹,以及利用分运动判断合运动

阅读理解

For Sparky, school was all but impossible. He failed every subject in the eighth grade. He flunked physics in high school, getting a grade of zero. Sparky also flunked Latin, algebra and English. He didn't do much better in sports. Although he did manage to make the school's golf team, he promptly lost the only important match of the season. There was a consolation(安慰) match; he lost that, too.

Throughout his youth Sparky was awkward socially. He was not actually disliked by the other students; no one cared that much. He was astonished if a classmate ever said hello to him outside of school hours. There's no way to tell how he might have done at dating. Sparky never once asked a girl to go out in high school. He was too afraid of being turned down.

Sparky was a loser. He, his classmates...everyone knew it. So he rolled with it. Sparky had made up his mind early in life that if things were meant to work out, they would. Otherwise he would content himself with what appeared to be his inevitable mediocrity(平凡).

However, one thing was important to Sparky - drawing. He was proud of his artwork. Of course, no one else appreciated it. In his senior year of high school, he submitted some cartoons to the editors of the Yearbook. Although the cartoons were turned down., Sparky was so convinced of his ability that he decided to become an artist.

After completing high school, he wrote a letter to Walt Disney Studios. He was told to send some samples of his artwork, and the subject for a cartoon was suggested. Sparky spent a great deal of time o it. Finally, the reply came from Disney Studios. He had been rejected once again. Anther loss for the loser.

So Sparky decided to write his own autobiography(自传) in cartoons. He described his childhood - a little boy loser and chronic underachiever. The cartoon character would soon become famous worldwide. For Sparky, the boy who had such a lack of success in school and whose work was rejected again and again, was Charles Schultz. He created the Peanuts comic strip(连环漫画) and the little cartoon character whose kite would never fly and who never succeeded in kicking a football--Charlie Brown.

68.From the first paragraph we can see that Sparky was       in high school.

A.a failure   B.an artist    C.a good player   D.a top student

69.Sparky never asked a classmate to go out with him because he was afraid of     .

A.making mistakes      B.making friends

C.being refused          D.being invited

70.In his senior year, Sparky felt confident that he had ability to         .

A.play golf  B.draw cartoons   C.learn English    D.write novels

71.His only success mentioned in this passage is       .

A.his golf match in high school  B.his artwork sent to the Yearbook

C.his subjects in the senior year  D.his autobiography in cartoons

72.From the passage we can infer that Sparky is a         person.

A.weak B.proud       C.disabled    D.determined

单项选择题 A1型题