问题 选择题

两辆发动机功率相同且恒定、质量不同的汽车,在平直路上行驶时,所受的阻力与车重成正比,下列结论正确的是

A.两车达到的最大动能相同

B.车的最大速率与质量成反比

C.两车具有相同的最大速率

D.车达到最大速率时合外力为零

答案

BD

设功率都为P,两车的质量分别为,则当车受到的空气阻力等于牵引力时即合外力为零时车达到最大速度,D正确。所以,即两车的最大速率分别为,即车的最大速率与质量成反比,B正确C错误。根据可得两车的最大动能不同,A错误。

多项选择题 案例分析题
阅读理解

New York Time —A gunman killed eight people at a mall in Omaha this afternoon and then killed himself,  setting off panic among holiday shoppers,  the police said.

“The person who we believe to be the shooter has died from self-inflicted gunshot wounds, ” Sgt. Teresa Negron of the Omaha Police Department said at televised news.  “We have been able to clear the mall, ” she said. “We don’t believe we have any other shooters. ” The police said that at least five other people had been injured in the shootings. 

She did not give the shooter’s identity. “We are still doing the investigation, ” Sergeant Negron said, adding that the city’s mayor, who was out of town, was on his way back to Omaha.

She said the police received a 911 call from someone inside the Westroads Mall on the west side of Omaha, and shots could be heard in the background. The first police officers arrived at the mall six minutes after the first call, she said, but by then the shootings were over.

It is reported that the gunman left a suicide note that was found at his home by relatives. A law enforcement official who spoke on condition of anonymity (匿名) said the note indicated that the gunman wanted to "go out in style".

The shootings broke the usually banal routine of holiday shopping. The gunman was said by some witnesses to have fired about 20 shots into a crowd. Some customers and workers ran screaming from the mall, while others dived into dressing rooms to hide from the shooter.

Shoppers and store workers were trapped inside the mall, which has roughly 135 stores. Others streamed out of mall exits with their hands raised. President Bush was in Omaha this morning to deliver a speech, but he had left the city by the time the shootings took place.

小题1:Where did the shootings first come out?

A.On a newspaper.

B.In the Internet.

C.In TV news.

D.In a police poster.小题2:What do the underlined words “go out in style” probably mean?

A.Go out of the mall in particular clothes.

B.Walk in the mall with everybody focused on.

C.Go to a socially event by fashionable means.

D.Stop his life in an impressive way.小题3:Which of the following is TRUE according to the passage?

A.Nobody knows why the shooter did so and nothing was found at his home.

B.The city’s mayor happened not to be in the city when the shootings took place.

C.Police arrived at the mall before the shootings were over and rescued customers.

D.The official who showed what the note meant had no request of his own identity.小题4:Which of the following can be the best title of the news?

A.Gunman Kills 8 People, Then Himself at a Mall in Omaha

B.Shoppers in Great Panic before the Holiday

C.Bush Happened to Escape a Shot

D.Shooter Found Dead in a Mall on the west of Omaha