问题 选择题

如图所示,顶端装有定滑轮的斜面体放在粗糙水平地面上,A、B两物体通过细绳连接,并处于静止状态(不计绳的质量和绳与滑轮间的摩擦).现用水平向右的力F作用于物体B上,将物体B缓慢拉高一定的距离,此过程中斜面体与物体A仍然保持静止.在此过程中(  )

A.水平力F一定变小

B.斜面体所受地面的支持力一定不变

C.地面对斜面体的摩擦力一定变大

D.物体A所受斜面体的摩擦力一定变大

答案

取物体B为研究对象分析其受力情况如图,

则有F=mgtanθ,T=

mg
cosθ
,在物体B缓慢拉高的过程中,θ增大,则水平力F随之变大.

对A、B两物体与斜面体这个整体而言,由于斜面体与物体A仍然保持静止,拉力F增大,则地面对斜面体的摩擦力一定变大,但是因为整体竖直方向并没有其它力,故斜面体所受地面的支持力应该没有变;在这个过程中尽管绳子张力变大,但是由于物体A所受斜面体的摩擦力开始并不知道其方向,故物体A所受斜面体的摩擦力的情况无法确定.故B、C正确,A、D错误.

故选BC.

单项选择题 共用题干题
阅读理解

                            

It’s an image that might make Saddam Hussein proud.A frightened prisoner,head covered and dressed in rags,electrodes attached to the fingers of his out-strectched hands.He’s been forced to stand on a box and,if he falls off,his captors have told him that he’ll be electrocuted(触电致死).

The prisoner was an Iraqi and his torturers were American soldiers who were sent to the country to liberate the Iraqi people.This unpleasant image was one of a series of photographs leaked by a US soldier.He was working at a US Prisoner of War(POW) camp,which used to be Saddam’s punishment centre.Since the pictures were shown on the American news programmer “60 Minutes Ⅱ” on April 28,they have caused shock and anger in the US and abroad.Despite US President George W. Bush’s promise to punish the responsible soldiers,the country’s image in the Middle East could be damaged forever.

“The liberators are worse than the dictators,”said Abdel-Bari Atwan,editor of the Arab newspaper Al Quds Al Arabi.“They have not just lost the hearts and minds of Iraqis but of people in all developing countries.”

UN secretary-General Kofi Annan said he was “deeply disturbed” by the pictures and hoped it was a single incident.However,similar photographs have appeared in British newspapers of British soldiers torturing Iraqis.

Any kind of torture, or mistreatment of prisoners is forbidden under the Geneva Conventions.

The first agreement was signed by 16 European countries in 1864 in Geneva,Switzerland.It was intended to protect wounded soldiers on land and limit human suffering in times of armed conflict.Further rules were added to cover the treatment of soldiers at sea,and prisoners of war.The entire set was accepted in 1949 and has since been accepted by nearly 200 countries.

57.The passage is about________.

A.how American soliders treated POWs

B.America’s global image

C.photos of POW mistreatment

D.international reactions to the photos being released

58.Why might such photos make Saddam Hussein proud?

A.He could be crueler than the torturers in the photo.

B.It showed the so-called liberators were worse than him.

C.They were taken in his punishment centre.

D.They could damage the image of the US in the Middle East forever.

59.According to the article,who had a hand in the mistreatments of Iraqi soldiers?

A.Saddam Hussein.           B.British soldiers.

C.American soldiers.         D.Both B and C.

60.Which of the following is wrong about the Geneva Conventions?

A.Over 200 countries have accepted the Conventions so far.

B.They make sure wounded soldiers get proper treatment.

C.They were named after the place where the first agreement was signed.

D.The Conventions show that the US soldiers acted wrongly.