问题 选择题

质量为m、电荷量为Q的带正电小物块在磁感应强度为B、方向垂直纸面向里的匀强磁场中,沿动摩擦因数为μ的绝缘水平面以初速度v0开始向左运动,如图12所示,经t时间走了s距离,物块停了下来.设此过程中q不变,则(  )

图12

A.①③

B.②③

C.①④

D.②④

答案

A

物体速度减小,受洛伦兹力减小,故水平面对物块支持力减小,摩擦力减小,故①③正确.

单项选择题

The past few years have been busy ones for human-rights organisations. In prosecuting the so-called war on terror, many governments in Western countries where freedoms seemed secure have been tempted to nibble away at them, while doughty campaigners such as Amnesty International (国际特殊组织) also exist for defence. Yet Amnesty no longer makes the splash it used to in the rich world. The organisation is as vocal as it ever was. But some years ago it decided to dilute a traditional focus on political rights by mixing in a new category called social and economic rights.

You might suppose that the more of rights you campaign for the better. Why not add pressing social and economic concerns to stuffy old political rights such as free speech and free elections What use is a vote if you are starving Are not access to jobs, housing, health care and food basic rights too No: few rights are truly universal, and letting them multiply weakens them.

Food, jobs and housing are certainly necessities, but there’s no use to call them "rights". When a government looks someone up without a fair trial, the victim, perpetrator and remedy are pretty clear. This clarity seldom applies to social and economic "rights". Who should be educated in which subjects for how long at what cost in taxpayers’ money is a political question best settled at the ballot box (投票箱). And no economic system known to man guarantees a proper job for everyone all the time.

It is hardly an accident that the countries keenest to use the language of social and economic rights tend to be those that show least respect for rights of the traditional sort. And it could not be further from the truth. For people in the poor world, as for people everywhere, the most reliable method yet invented to ensure that governments provide people with social and economic necessities are called politics. That is why the rights that make open polities possible — free speech, due process, protection from arbitrary punishment— are so precious. Insisting on their enforcement is worth more than any number of grandiloquent but unenforceable declarations demanding jobs, education and housing for all.

Many do-gooding outfits suffer from having too broad a focus and too narrow a base. Amnesty used to appeal to people of all political persuasions and none, and concentrate on a hard core of well-defined basic liberties. However, by trying in recent years to borrow moral authority from the campaigns and leaders of the past and lend it to the cause of social reform, Amnesty has succeeded only in muffling what was once its central message, at the very moment when governments in the West need to hear it again.

The underlined word "grandiloquent" (Line 6, Paragraph 4) most probably means ()

A. glorious

B. eloquent

C. exaggerated

D. excellent

单项选择题