问题 选择题

如图,在“验证力的平行四边形定则”的实验中,使弹簧秤乙从图示位置开始沿顺时针方向开始缓慢转动,在此过程中保持结点O的位置不变,保持弹簧秤甲的拉伸方向不变。那么,在全过程中,关于弹簧秤甲、乙的示数F1、F2变化是 ( )

A.F1增大,F2减小

B.F1减小F2增大

C.F1减小,F2先增大后减小

D.F1减小,F2先减小后增大

答案

答案:D

以O为研究对象,弹簧拉力与F1、F2合力为0,可构成封闭三角形,由动态分析可知F1减小,F2先减小后增大,D对。

单项选择题
单项选择题

For the first time, George Bush has acknowledged the existence of secret CIA prisons around the world, where key terrorist suspects—100 in all, officials say—have been interrogated with "an alternative set of procedures". Fourteen of the suspects, including the alleged mastermind of the September 11th attacks, were transferred on Monday to the American naval base at Guantánamo Bay in Cuba, where some will face trial for war crimes before special military commissions.

Many of these men—as Mr. Bush confirmed in a televised speech at the White House on September 6th—are al-Qaeda operatives or Taliban fighters who had sought to withhold information that could "save American lives". "In these cases, it has been necessary to move these individuals to an environment where they can be held secretly (and) questioned by experts," the president said. He declined to say where they had been held or why they had not simply been sent straight to Guantánamo, as some 770 other suspected terrorists have been.

Mr. Bush also refused to reveal what interrogation methods had been used, saying only that, though "tough", they had been "safe and lawful and necessary". Many believe that the main purpose of the CIA’s prisons was to hide from prying eyes the torture and other cruel or degrading treatment used to extract information from prisoners. But Mr. Bush insisted that America did not torture : "It’s against our laws, and it’s against our values. I have not authorised it—and I will not authorise it."

The Pentagon this week issued its long-awaited new Army Field Manual, forbidding all forms of torture and degrading treatment of prisoners by army personnel—though not the CIA. For the first time, it specifically bans forced nakedness, hooding, the use of dogs, sexual humiliation and "waterboarding" (simulated drowning )—all practices that have been used at Guantámamo and Abu Ghraib.

So why did the president decide now to reveal the CIA’s secret programme Partly, he confessed, because of the Supreme Court’s recent ruling that minimum protections under the Geneva Conventions applied to all military prisoners, no matter where they were. This has put American agents at risk of prosecution for war crimes. Mr. Bush has now asked Congress to ban suspected terrorists from suing American personnel in federal courts.

Mr. Bush’s attitude toward the public’s remarks is()

A.consent

B. hesitation

C.denial

D. approval