问题 选择题

将一金属块挂在竖直的弹簧测力计挂钩上,并处于静止状态.金属块所受的重力为G,金属块对弹簧测力计的拉力为F1,弹簧测力计对金属块的拉力为F2,下列说法正确的是(  )

A.F1与F2是一对平衡力

B.G与F2是一对平衡力

C.G与F1是一对平衡力

D.G与F1是一对相互作用力

答案

A、金属块对弹簧测力计的拉力为F1和弹簧测力计对金属块的拉力为F2,二者分别作用在弹簧测力计和金属块上,大小相等、方向相反、在同一直线上,属于一对相互作用力,该选项说法不正确;

B、金属块所受的重力为G和弹簧测力计对金属块的拉力为F2,这两个力都是作用在金属块上,大小相等、方向相反、在同一直线上,属于一对平衡力,该选项说法正确;

C、金属块所受的重力为G和金属块对弹簧测力计的拉力为F1,这两个力方向相同,既不属于平衡力也不属于相互作用力,故CD都不正确.

故选B.

阅读理解

Spider-Man cannot escape the harsh realities of the current economic times and will lose his job in a latest issue of the Amazing Spider-Man hitting stories ( first published in 1963) this week.

Peter Parker, official photographer of the mayor by day and New York City crime fighter by night, is going to face new challenges, including unemployment.

"He's going to struggle with unemployment and trying to save the city while he can barely afford to keep a roof over his head," said Steve Wacker, Marvel Comics senior editor.

Parker has always been a grounded character with real-world problems, Wacker said. His aunt is frequently sick, he has girlfriend troubles, and he sometimes struggles to find work. In addition, Spider-Man story lines are often set against a backdrop of current events.

In the near future, Parker will have to juggle paying bills and buying "web-fluid" and other materials to fix his superhero costume in addition to keeping his dual identities under wraps.

Parker's work history includes photographer, assistant high school coach, science teacher and scientific researcher, according to his biography on the Marvel Web site. His education includes a college degree in biophysics and some postgraduate work in biochemistry.

It was at a science exhibit he attended as a teenager that he was bitten by a radioactive spider and got the creature's strength, agility and weaving ability, says Marvel Comics.

And although Parker has skills few others can claim, he probably won't list these on his resume: superhuman strength, ability to cling to most surfaces, fast traveling ability aided by web-slinging and spider-sense danger avoidance system.

49. According to the story, Parker is likely to________.

A. look for another job.

B. have a girlfriend.

C. live in a large  house.

D. buy a new superhero costume.

50. Parker didn’t work as________.

A. a photographer.  B. an assistant coach   C. a science teacher.  D. a spider-man

51. The underlined part in the third paragraph means:

A. he has a roof over his head

B. he has a room to live in

C. there is a roof in his head

D. he has a picture of a roof in his head.

52. This passage mainly tell us _______.

A. Parker is a   spider-man.

B. how Parker became a spider-man.

C. life is hard for everyone in current economic times.

D. the amazing spider-man comic is popular until now. 

多项选择题