问题 问答题

质量为m的小球A以水平速度v与原来静止在光滑水平面上的质量为3cm的小球B发生正碰,已知碰撞过程中A球的动能减少了75%,求碰撞后B球的速度.

答案

Ek=

1
2
mv2可知,A球碰后的速度vA
v
2

由于A、B碰撞过程中动量守恒,所以mv=mvA+3mvB

解得:当vA=

v
2
时,vB=
v
6
,当vA=-
v
2
时,vB=
v
2

由于第一组答案不符合实际运动情况,应舍去,所以碰后B球的速度为

v
2

答:碰后B球的速度为

v
2

单项选择题 A1/A2型题
阅读理解

阅读理解。

     More than one in ten UK teenagers has been left without a job or college place, despite 11 years of

compulsory education, figures show.

     The number of 16-t0 18-year-olds branded as "Neet"-not in education, employment or training-has

risen amid growing fears that school-leavers are bearing the brunt of job shortages in the recession.

     Some 261,000 young people had no job or training place, according to official data. The figure rose

to 1,082,000 among 16-to 24-year-olds.

     The Conservatives branded the figure "shocking".

     David Willetts, the shadow skills secretary, said:"It is a damning indictment of the Government's

failure to help young people during the recession." 

     "Despite all Cordon Brown's guarantees and pledges, the number of young people neither earning nor

learning is increasing at a rate of more than 9,000 a week. Ministers must stop making empty gestures

that do so little to help young people."

     The Government has a target to reduce the proportion of young Neets to 7.6 per cent by next year.

     The latest annual data from the Department for Children, Schools and Families put the figure at 10.3

per cent by the end of 2008.

     The percentage of 16-t0 18-year-olds who fall into the same bracket remained higher in the past year

than in the previous 12 months, it was revealed.

     "In a further disclosure, figures for the third quarter of this year show almost a fifth of 16 to 24-year-

olds were in the category-more than at any point since 2005.

     Iain Wright, the Schools Minister, said:"We are giving all l6 and 17-year-olds the opportunity to stay

in education or training so they can gain the skills they need to succeed in an increasingly competitive

labour market."

     "We must not repeat the mistakes that were made in recessions of the past and abandon a whole

generation of young people. We recognize that we need to carry on helping young people through this

tough economic climate."

     He said the Government would offer every Neet 16 and 17-year-old a place on an "Entry to Employment"

course in January.

1. According to what David Willetts said, the number of young people neither earning or learning will increase

    ____ in a year.

A. 261,000

B. 1,082,000

C. 9,000

D. 432,000

2. The author develops the passage mainly by ____.

A. providing typical examples

B. telling an interesting story

C. comparing opinions from different fields

D. presenting a problem and possible solutions

3. What David Willetts said indicates that ____.

A. the government has tried its best to solve the problem

B. the problem is unavoidable during the recession

C. what the government has done is far from satisfactory

D. he is sure the government can solve the problem

4. Which of the following is NOT true according to Iain Wright?

A. The government has realized how serious the problem is and will take effective measures.

B. Young people are facing a tough economic climate.

C. The government responded too late in face of the situation.

D. It will be difficult for young people to be employed if they don't have relevant skills.