问题 选择题

已知两个质点相距r时,它们之间的万有引力大小为F;若将它们之间的距离变为2r,则它们之间的万有引力大小为(  )

A.4F

B.2F

C.

1
4
F

D.

1
2F

答案

根据万有引力定律得:

甲、乙两个质点相距r,它们之间的万有引力为F=G

Mm
r2

若保持它们各自的质量不变,将它们之间的距离增大到2r,

则甲、乙两个质点间的万有引力F′=G

Mm
(2r)2
=
1
4
F

故选C.

名词解释
阅读理解

Twelve years ago, when I was 50,I wondered what 60 or 70 would be like? I looked around and saw only one style of living. It’s not fair, I thought. Young people have so many styles to choose from, but older people have just one choice. So I decide to do something about it , something practical.

I worked on my fitness by joining exercise classes in town. A few years later, my husband and I moved to a retirement community, and I wanted to teach aerobic(有氧运动的)classes. The community center wouldn’t give me a room to teach in, so I had to walk around and find any available empty room.

One day, the community center staff came to me and asked if I would help with the entertainment for a Hawaiian luau(夏威夷式宴会)they were putting on. I said yes. Then I talked five other ladies into dancing with me. We performed the hula(呼啦舞)and a war chant and brought the house down. Someone had a camera and took pictures, and then sent them to our local paper. We got requests for more engagements, which in turn led to more publicity and yet more engagements. Soon we had invitations from all over the country. The Dancing Grannies were born!

I think the real secret of the Dancing Grannies is out attitude. I was raised extremely poor ---no-food poor. If we wanted toys we had to make things up to play with ,so I learned early to be very creative. And you know,I think being poor was one of the best things that ever happened to me because I learned to look for treasures.

That’s what I’m still doing today—looking for the treasure in growing old. I’m getting better and better.

It’s true that antiques have to be treated a bit differently, with a little care, but they still have a beauty of their own. 

小题1:What did the writer think of the living style of the older people when she was 50?

A.Unsatisfying

B.Favorable

C.Pleasant

D.Practical小题2:Why did the writer have to walk around and find an empty room?

A.Because she couldn’t offer an expensive room.

B.Because she wasn’t given a room to teach in by the community center.

C.Because she wanted to find a better one.

D.Because she wanted to keep fit by walking.小题3:What can we infer from the writer’s performance?  

A.It was just so-so.

B.It was a failure.

C.It was average.

D.It was a success.小题4:What made the writer learn to look for treasures?

A.Being active

B.Being creative

C.Being rich

D.Being poor小题5:What does the underlined word “antiques” (in the last paragraph) refer to?  

A.Ancient treasures

B.Poor children

C.Old people

D.The Dancing Grannies