问题 计算题

(9分)2004年1月4日美国“勇气”号火星车在火星表面成功登陆。登陆时机选择在6万年来火星距地球最近的一次,火星与地球之间的距离仅有5580万千米,如图所示。火星车在登陆前绕火星作圆周运动,距火星表面高度为H,火星半径为R,绕行N圈的时间为t,求:

(1)若地球、火星绕太阳公转均为匀速圆周运动,通过计算比较它们周期T、T大小;

(2)火星的平均密度(用R、H、N、t、引力常数G表示);

(3)火星车登陆后不断地向地球发送所拍摄的照片,地球上接收到的第一张照片大约是火星车多少秒前拍摄的?

答案

(1)因为,故:(2)(3)

题目分析:(1)由得:

   因为,故:

(2)由

  联立得:

(3) 

点评:本题考查了利用万有引力定律提供向心力的例题。在学习时要知道库仑定律的含义的理解。

阅读理解

Three quarters of Britain’s parents are too busy to read bedtime stories to their children,according to a study. The study was carried out by CITV to start their new children’s show Bookaboo,which is designed to encourage anyone to pick up a book and read with their children at any time of the day.

Worryingly,the study showed that only three percent of fathers now find the time to read to the kids compared to 89 percent of mothers. Lucy Goodman,creator of Bookaboo,said,“It’s important for young boys to be able to share a book with dads,granddads or male carers and it can be fun and rewarding,too.” Of the dads who said they didn’t read to their kids,87 percent blamed work while more than a third said they were too tired. While 89 percent of mums said they did read to their children,more than half of them said cleaning distracted (使分心) them and 49 percent were distracted by other household things.

Researchers also found parents are now relying heavily on other people to lend a hand with reading to their children with grandparents doing the most,followed by sisters and brothers,aunts and uncles. While 95 percent of parents read to their children at some point,only five percent read to their children during the day. More than one in ten said they read every couple of weeks or less,and five percent could not remember the last time they shared a book.

The study found parents also seem content with allowing their children to immerse (使沉浸) themselves in TV programs or playing computer games rather than reading.

Ex­goalkeeper David Seaman,who is a dad of two,has been a guest in Bookaboo.He says,“I think it’s important that fathers do read to their children because it’s a special time. Sometimes my two children will come to listen to the same book—it’s a magical moment and I advise fathers just to try it.”

小题1:We can know from the passage that Bookaboo________.

A.is a daily show

B.is an adults’ show

C.is a popular show

D.aims to encourage people to read to their children小题2:According to the study,fathers don’t read to their kids mainly because________.

A.they are too busy with work

B.they don’t think it necessary to do so

C.they are distracted by household things

D.they like to play computer games in their free time小题3:Which group of people helped parents read to the kids the most?

A.Aunts and uncles.

B.Grandparents.

C.Children’s carers.

D.Children’s sisters and brothers.小题4:According to the last paragraph,David Seaman________.

A.is a goalkeeper now

B.has only one child

C.is the creator of Bookaboo

D.thinks it is great to read to children

问答题 案例分析题