问题 选择题

如图,在灭火抢险的过程中,消防队员有时要借助消防车上的梯子爬到高处进行救人或灭火作业。为了节省救援时间,消防车向前前进的过程中,人相对梯子匀加速向上运动,在地面上看消防队员的运动,下列说法中正确的是(   )

A.当消防车匀速前进时,消防队员可能做匀加速直线运动

B.当消防车匀速前进时,消防队员水平方向的速度保持不变

C.当消防车匀加速前进时,消防队员一定做匀变速曲线运动

D.当消防车匀减速前进时,消防队员一定做匀变速曲线运动

答案

答案:D

消防员参与了沿梯子方向的匀加速直线运动和水平方向上的匀速直线运动,通过合速度与合加速度是否在同一条直线上判断消防员做直线运动还是曲线运动.若消防车匀速前进,根据运动的合成,知合速度的方向与加速度的方向不在同一条直线,其加速度的方向大小不变,所以消防员做匀变速曲线运动,故A错误

将消防员的运动分解为水平方向和竖直方向,知水平方向上的最终的速度为匀速后退的速度和沿梯子方向速度在水平方向上的分速度的合速度,因为沿梯子方向的速度在水平方向上的分速度在变,所以消防队员水平方向的速度在变。故B错误

若消防车匀加速前进,根据运动的合成,知合速度的方向与合加速度的方向有可能在同一条直线,其加速度的方向大小不变,所以消防员有可能做匀变速直线运动,故C错误

若消防车匀减速前进,根据运动的合成,知合速度的方向与合加速度的方向不在同一条直线,其加速度的方向大小不变,所以消防员做匀变速曲线运动,故D正确

阅读理解

XI’AN---Seven people died in a fire early on Wednesday morning in Xi’an, capital of Shanxi Province. A restaurant with a karaoke hall in the southern suburbs caught fire around 2 a. m. and seven waitresses who were sleeping on the second floor of the restaurant were killed. The restaurant was completely destroyed and the waitresses, the local police said, were killed by toxic smoke from burning decorations.

MANILA---Four people were killed yesterday in the central Philippine island of Tacloban when a bomb they had dug up exploded, local police were quoted as saying. The four people were digging to set up a septic(poisonous)tank in their house when they dug up the bomb. It went off, killing all four people, local police were quoted by radio station DZBB as saying. The police did not say where the bomb came from. Unexploded bombs from World War II are still discovered around the Philippines once in a while.

TEL AVIV---An Israeli couple kissed for 30 hours and 45 minutes which, a spokeswoman said yesterday, was a world record. The couple, both in their twenties, started kissing on Monday at 8:30 p.m. along with 250 other couples in a contest. “For nearly 31 hours they didn’t eat, drink, talk or even go to the bathroom. And the whole time, they were standing up”, said Arielle Goldman, who handled public relations for the event. She said a representative of the Guinness Book of World Records was on hang to witness the event, recorded on video. The previous record was 29 hour and 37 minutes, Goldman said. The winning couple received two round-the-world plane tickets and $2,500. (277 words)

小题1:Which of the following statements is right?

A.The news report didn’t mention the loss caused by the fire.

B.After reading the report we know how the fire broke out.

C.The reporter tended to think the bomb had something to do with World War II

D.The police refused to admit the bomb had anything to do with World War II.小题2: The underlined word “toxic” means _____.

A.poisonous

B.dangerous

C.hot

D.thick小题3: The Israeli couple kissed for nearly 31 hours_____.

A.to test their endurance

B.to set a new world record

C.to show their special love

D.to prove they are very healthy小题4:Why did so many couples take part in the contest?

A.Because it was a good chance to enjoy themselves.

B.Because they were poor and wanted to gain the 2,500 dollars.

C.Because they wanted to attract people’s attention.

D.Because they aimed at the honor and prize.

选择题