问题 问答题

我国发射的“嫦娥一号”卫星发射后首先进入绕地球运行的“停泊轨道”,通过加速再进入椭圆“过渡轨道”,该轨道离地心最近距离为L1,最远距离为L2,卫星快要到达月球时,依靠火箭的反向助推器减速,被月球引力“俘获”后,成为环月球卫星,最终在离月心距离L3的“绕月轨道”上飞行.已知地球半径为R,月球半径为r,地球表面重力加速度为g,月球表面的重力加速度为g/6,求:

(1)卫星在“停泊轨道”上运行的线速度;

(2)卫星在“绕月轨道”上运行的线速度.

答案

(1)根据万有引力提供向心力G

Mm
L12
=m
v12
L1
        

解得:v1=

GM
L1

在地球表面的物体受到的重力等于万有引力G

Mm
R2
=mg

解得:GM=R2g

所以  v1=

gR2
L1

(2)根据万有引力提供向心力 G

Mm
L32
=m
v22
L3
   

解得:v2=

GM
L3

在月球表面的物体受到的重力等于万有引力G

Mm
r2
=mg

解得:GM=r2g=

1
6
gr2

所以v2=

gr2
6L3

答:(1)卫星在“停泊轨道”上运行的线速度为

gR2
L1

(2)卫星在“绕月轨道”上运行的线速度为

gr2
6L3

完形填空

A girl went to her father to ask for his suggestion. She was having a        time in life, and it seemed that as soon as one problem disappeared another one         in its place.

Her father, a chef, took her into the kichen. He poured water into three pans and put them on to boil. After the water boiled, he put some carrots into the first pan, some         into the second pan and coffee into the last one. He waited without saying a word.

After 20 minutes, her father turned         the stove(炉子), took out the carrots and the eggs and put them in a bowl. He poured the coffee into a cup.

He asked his daughter, “Dear,         do you see?”

“Carrots, eggs, and coffee”, she replied.

“Touch the carrots,” he told her. She did and felt that the carrots were       . After that he asked her to take an egg and break it. She found that the egg was hard.       , her father asked her to taste the coffee.

She asked, “What’s the          , Father?”

Her father said, “As you see, each thing reacted(起反应) differently to the boiling water. The strong and hard carrots became soft and weak after boiling. The fragile(脆弱的) eggs became hard after being cooked. The coffee beans were very special, but they changed in the water, too.”

“Who are you?”asked her father. “When trouble          at your door, how do you react? Are you carrots, eggs,          coffee?”

小题1:A. hard                      B. happy                 C. busy

小题2:A. happended                 B. took                  C. appeared

小题3:A. meat                      B. fish                  C. eggs

小题4:A. on                        B. off                   C. over

小题5:A. what                      B. why                  C. how

小题6:A. delicious                   B. crispy                C. soft

小题7:A. At once                    B. At last                C. At present

小题8:A. meaning                   B. reason                C. consequence

小题9:A. shouts                    B. stares                C. knocks

小题10:A. and                     B. or                   C. but

单项选择题