问题 问答题

某同学做探究“合力的功和物体速度变化关系”的实验装置如图,小车在橡皮筋作用下弹出,沿木板滑行.用一条橡皮筋时对小车做的功记为W,当用2条、3条…,完全相同的橡皮筋并在一起进行第2次、第3次…实验时,每次实验中橡皮筋伸长的长度都保持一致.实验中小车获得的速度由打点计时器所打的纸带测出.

(1)木板水平放置,小车在橡皮筋作用下运动,当小车速度最大时,关于橡皮筋所处的状态与小车所在的位置,下列说法正确的是(  )

A.橡皮筋仍处于伸长状态            B.橡皮筋恰好恢复原长

C.小车恰好运动到两个铁钉的连线处  D.小车已超过两个铁钉的连线

(2)如图所示是某次正确操作情况下,在50HZl作电源下打点计时器记录的一条纸带,为了测量小车获得的速度,应选用纸带的______(填AF或FI)部分进行测量,速度大小为______m/s.

答案

(1)平衡摩擦力后,橡皮筋的拉力等于合力,橡皮条做功完毕,小车的速度最大,若不进行平衡摩擦力操作,则当橡皮筋的拉力等于摩擦力时,速度最大,本题中木板水平放置,显然没有进行平衡摩擦力的操作,因此当小车的速度最大时,橡皮筋仍处于伸长状态,故BCD错误,A正确.

故A正确.

(2)小车先加速,后匀速,最后减速运动,在加速过程中,橡皮条在做正功,故需要测量最大速度,即匀速运动的速度,因而需要选用间隔均匀的点,即FI之间的点,打点计时器每隔0.02s打一次点,故最大速度为:v=

x 
T
=
1.52cm
0.02s
=0.76m/s

故答案为:FI,0.76.

选择题
阅读理解

It is impossible to think about “growing up” in modern America without considering “youth culture” which every young person—even those who do not attend public schools—is confronted by and must deal with. It is impossible to be so isolated that we are untouched by the surrounding culture. Nor should we wish to be—as we are called to be—salt and light in a very confused and broken world. Popular culture deserves neither uncritical acceptance nor knee-jerk rejection, but thoughtful critique(批评).

On the contrary, China paid too little attention to youth culture in the past. However, with society developing, more and more people have realized the importance of analyzing, understanding and promoting youth culture.

About 100,000 young Chinese people from all over the world will attend the first China Youth Culture Week scheduled to open Saturday in Shenzhen’s China Folk Culture Villages, a press conference was told Thursday.

A series of cultural activities will be staged from Saturday to Wednesday, including a huge performance expected to challenge for a listing in the Guinness Book of World Records.

About 10,000 young people will attend the opening ceremony Saturday. A final list of the Chinese Youth Idol Award to five outstanding young Chinese was announced at the conference. They are the country’s first astronaut, Yang Liwei, Chinese NBA star, Yao Ming, IT entrepreneur, Ding Lei, anchorperson, Wu Xiaoli, and Olympic Games gold medalist, Deng Yaping. The youth idols were selected by

Chinese teenagers with 380,000 votes cast nationwide.

During the past two months, the organizers received more than 3,000 applications from young people in Hong Kong and Macao who wanted to take part in the performance.

52. Which of the following can replace the underlined word “confronted by”?

A. Concerned about.        B. Thought of.  C. Confused with.    D. Faced with.

53. Which of the following is TRUE according to Paragraph 1?

A. People can be isolated from the surrounding culture.

B. The American youth accept popular culture without any thought.

C. People shouldn’t refuse popular culture totally.

D. Americans ignore cultures at all while growing up.

54. The list of the five Chinese youth idols indicates that ____.

A. success is considered the most important factor in the Chinese youth’s values

B. the Chinese youth don’t care about their idols’ personalities

C. there are only five people admired by the Chinese youth

D. the parents want to set those people as examples

55. What can we infer from this passage?

A. America paid too much attention to youth culture.

B. China pays more attention to youth culture nowadays.

C. Chinese youth admire movie stars and regard them as their idols.

D. America thinks their youth are more important than the Chinese youth.