问题 多选题

从1984年我国第一颗试验同步卫星发射成功到2005年神舟五号载人飞行,我国的航天事业实现了两次质的飞跃.神舟五号历经21小时27分37秒,绕地球运行14圈后安全着陆.则运行时神舟五号与同步卫星相比(  )

A.神舟五号比同步卫星的加速度小

B.神舟五号比同步卫星的线速度大

C.神舟五号比同步卫星离地高度大

D.神舟五号比同步卫星角速度大

答案

根据万有引力提供向心力,则得:G

Mm
r2
=man=mω2r=m
v2
r
=m
4π2
T2
r

则得T=2π

r3
GM
,v=
GM
r
,ω=
GM
r3
,an=
GM
r2
.可见,轨道半径越大,加速度越小,周期越大,线速度越小,角速度越小.

由于同步卫星的周期必须与地球自转周期相同,为24h,大于神舟五号的周期,则根据上面等式得出:神舟五号半径小于同步卫星的半径,所以神舟五号的加速度大,线速度大,高度大,角速度大,故AC错误,BD正确;

故选BD

单项选择题 A1/A2型题
单项选择题

"Congratulations, Mr. Jones, it’s a girl. "

Fatherhood is going to have a different meaning and bring forth a different answer from every man who hears these words. Some feel proud when they receive the news, while others worry, wondering whether they will be good fathers. Although there are some men who like children and may have had considerable experience with them, others do not particularly care for children and spend little time with them. Many fathers and mothers have been planning and looking forward to children for some time. For other couples, pregnancy was an accident that both husband and wife have accepted willingly or unwillingly.

Whatever the reaction to the birth of a child, it is obvious that the change from the role of husband to that of father is a difficult task. Yet, unfortunately, few attempts have been made to educate fathers in this re-socialization process. Although many good books have been written about American mothers, only recently have some books discussed the role of a father.

It is argued by some writers that the transition to the father’s role, although difficult, is not nearly as great as the transition the wife must make to the mother’s role. The mother’s role seems to require a complete transformation of daily routine and adaptation to a new life, on the other hand, the father’s role is less demanding and immediate. However, even though we have mentioned the fact that growing numbers of women are working outside the home, the father is still thought by many as the breadwinner in the household.

Some writers argue that with respect to the change of roles, fathers, compared with mothers,()

A. have to do more in the household

B. have to make more difficult adaptations

C. have an easier job to do

D. can usually do a better job