问题 多选题

甲、乙两球质量相同,悬线一长一短,如将两球从图所示位置,同一水平面无初速释放,不计阻力,则小球通过最低点的时刻(  )

A.甲球的动能较乙球大

B.两球受到的拉力大小相等

C.两球的向心加速度大小相等

D.相对同一参考平面,两球机械能相等

答案

A、从同一水平面无初速释放到小球通过最低点的过程中运用动能定理可知:小球的末动能等于小球重力所做的功,而由题意可知甲下落的位移大,故甲球重力做的功多,故甲球的动能大于乙球的动能,故A正确;

B、在最低点有:F-mg=m

v2
l
,根据动能定理得:
1
2
mv2=mgl
,解得:F=3mg,与绳长无关,故B正确;

C、两球的向心加速度为:a=

v2
l
=2g,与绳长无关,故C正确;

D、相对同一参考平面,初始位置机械能相等,下落过程中机械能守恒,故到达C点时机械能相等,故D正确.

故选ABCD.

单项选择题
阅读理解

A serious problem for today's society is who should be responsible for our elderly and how to improve their Lives.It is not only a financial problem but also a question of the system we want for our society.I would like to suggest several possible solutions to this problem.

First, employers should take the responsibility for their retired employees.To make this possible, a percentage of profits should be set aside for this purpose. But when a company must take life-long responsibility for its employees, it may softer from a commercial disadvantage due to higher employee costs.

Another way of solving the problem is to return the responsibility to the individual.This means each person must save during his working years to pay for his years of retirement.This does not seem a very fair model since some people have enough trouble paying for their daily life without trying to earn extra to cover their retirement years.This means the government might have to step in to care for the poor.

In addition, the government could take responsibility for the care of the elderly.This could be financed through government taxes to increase the level of pensions.Furthermore, some institution should be created for senior daises, which can help provide a comfortable life for them.Unfortunately, as the present situation in our country shows, this is not a truly viable answer.The government can seldom afford to care for the elderly, particularly when it is busy trying to care for the young.

One further solution is that the government or social organizations establish some working places especially for the elderly where they are independent.

To sum up, all these options have advantages and disadvantages.Therefore, it is reasonable to expect that some combination of these options may be needed to provide the care we hope to give to our elderly generations.

小题1:What is the passage mainly about?

A.The problems faced by the old in society.

B.Why we should take responsibility for the old.

C.How we can improve the lives of the old.

D.Where the old can go to get their pensions.小题2:According to the passage, how can the government help to improve the lives of retired people?

A.Set aside some profits to help people with problems after they retire.

B.Increase savings levels of people during their working years.

C.Increase the discounts for food and transport for the old.

D.Make available pensions for those who have retired.小题3:The underlined word "viable" most probably means"_       ".

A.impossible

B.practical

C.useful

D.successful小题4:What can be concluded from the passage?

A.Taking care of the old is mainly an issue of money.

B.Employers should allow their workers to retire at a later age.

C.Becoming independent should be the goal of most old people.

D.There is no single solution to the problems of the old.小题5:What is the writer's main purpose in writing this article?

A.To point out the need for government support for old people.

B.To make general readers aware of the problems of retired people.

C.To discuss some possible solutions to an important social problem.

D.To instruct retired people on how they can have a happier life.