问题 问答题

2003年10月15日,随着“神州五号”载人飞船的发射升空,设飞船在离地面高度为h,在一圆形轨道上做匀速圆周运动,地球半径R,地球表面重力加速度为g.

求:(1)飞船在轨道上运行的速度大小?

(2)飞船运行的周期?

答案

(1)根据万有引力提供向心力,有:G

Mm
(R+h)2
=m
v2
(R+h)

所以:v=

GM
R+h

又因为地球表面的物体受到的重力等于万有引力G

Mm
R2
=mg,有:GM=R2g

故:v=

R2g
R+h

(2)根据万有引力提供向心力,有:G

Mm
(R+h)2
=m(
T
)2(R+h)

所以:T=2π

(R+h)3
GM

又因为:GM=R2g

故:T=2π

(R+h)3
R2g

答:(1)飞船在轨道上运行的速度大小为

R2g
R+h

(2)飞船运行的周期为

(R+h)3
R2g

阅读理解

This course is for those who want to learn to type, as well as those who want to improve their typing. The course is not common. You are tested in the first class, and begin practising at one of eight different skill levels. This allows you to learn at your own speed. Each program lasts 20 hours. Bring your own paper.

Course fee: $125      Materials:  $25

Two hours for each evening for two weeks. New classes begin every two weeks.

This course is taught by a number of professional business education teachers who have successfully taught typing course before.

UNDERSTANDING COMPUTERS

This twelve-hour course is for people who do not know very much about computers, but who need to learn about them. You will learn what computers are, what they can or can’t do and how to use them.

Course fee:$75  Jan 4,7,11,14,18  Wed.&Sat. 9:00---11:30 a.m.  Equipment fee:$10

David is a professor of Computer Science at Beijing University. He has over twenty years of experience in the computer field.  

STOP SMOKING

Do you want to stop smoking? Have you ever tried and failed? Now is the time to stop smoking using the latest methods. You can stop smoking, and this twelve-course will help you do it.

Course fee:$30  Jan 2,9,16,23   Mon 2:00---5:00 p.m.

Dr. John is a practicing psychologist who has helped hundreds of people stop smoking.

小题1:If you choose the UNDERSTANDING COMPUTERS course, you will have

classes_______.

A.twice

B.three times

C.four times

D.five times小题2:Mr. Black works every morning and evening, but he wants to take part in one of the three

courses. Your suggestion is __________.

A.TYPING

B.UNDERSTANDING COMPUTERS

C.STOP SMOKING

D.all the courses小题3:If you want to learn about computers, and at the same time you want to improve your

typing, you will pay  ______________.

A.$75

B.$150

C.$115

D.$235小题4:The special difference between the TYPING course and the other two is that __________.

A.people with different skill levels pay differently.

B.you will take a test in the first class for level decision

C.you will pay the fee before practicing typing.

D.you will pay less money for your study.

填空题