问题 多选题

2007年10月24日18时05分,我国成功发射了“嫦娥一号”探月卫星,11月5日进入月球轨道后,经历3次轨道调整,进入工作轨道.若该卫星在地球表面的重力为G1,在月球表面的重力为G2,已知地球半径为R1,月球半径为R2,地球表面处的重力加速度为g,则(  )

A.月球表面处的重力加速度g

G2
G1
g

B.月球的质量与地球的质量之比为

G1
R22
G2
R21

C.卫星在距月球表面轨道上做匀速圆周运动的周期T为2π

R2G1
gG2

D.月球的第一宇宙速度与地球的第一宇宙速度之比为

G1R2
G2R1

答案

A、卫星在地球表面的重力为G1,在月球表面的重力为G2,则

g
g
=
G2
G1
,所以g=
G2
G1
g
.故A正确.

    B、根据万有引力等于重力G

Mm
R2
=mg,知M=
gR2
G
.中心天体的质量与半径和表面的重力加速度有关.所以月球的质量和地球的质量之比
M
M
=
g
g
?
R22
R12
=
G2R22
G1R12
.故B错误.

    C、根据mg=mR2(

T
)2,得T=2π
R2
g
,而g=
G2
G1
g
,所以T=2π
R2G1
gG2
.故C正确.

   D、根据mg=m

v2
R
,知第一宇宙速度v=
gR
,而
g
g
=
G2
G1
,所以第一宇宙速度之比
v
v
=
G2R2
G1R1
.故D错误.

故选AC.

完形填空

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项,并在答题卡上将该选项的字母标号涂黑。选项中有两项为多余选项。

Easy ways to get healthy

I always hate the first few weeks of the new year, mostly because I-m sick to death of people in commercials who are all. "Let's diet !  It's a new year! "

You can always choose to switch it up! 小题1:Here are some simple ways to get your healthy on all year around.

Switch out bad habits for good ones. 小题2:Do something as simple as swapping nighttime cookies for nighttime vitamins.

Catch some sleep. One of the most important things we can do for our minds and bodies is to make sure. we're getting enough sleep on a regular schedule. 小题3:

Feed your mind. Keep your mind flexible and smart. Do crosswords, sudoku(数独). Start a new hobby, read a book about something you don't understand-anything that challenges you to think differently and exercise that brain of yours.

小题4:I'm not suggesting you take on a brand new fitness quest, but take the stairs, park farther away, and find a hobby you enjoy that allows you to be active..

Get organized. I'm not saying a whole repair of your entire world; start small. Organize a kitchen  cabinet.  Purge (清除 )yourself of stuff you  don't need.

Get rid of the mess. That means your mind is included too!  Make lists. Get a calendar and mark down important days. Clear your mind and your home. 小题5:

Smile. Overlook some of the bad things that are going on in your life. and focus on the good. There are positives in nearly every situation, even if it doesn't feel like it. Staying positive can help in nearly every aspect of your life!

A.Change your activity up.

B.Try exercising your brain too.

C.You'll find it improves your mood.

D.You are the one to improve yourself. E. lt’s time to take charge of your health!

F. Sounds boring, I know, but trust me --- sleep is amazing for you.

G. Start small, and don't plan to change your entire life in a week.

单项选择题