问题 选择题

地球赤道上的物体随地球自转而做圆周运动的向心力为F1,向心加速度为a1,线速度为v1,角速度为ω1;地球同步卫星的向心力为F2,向心加速度为a2,线速度为v2,角速度为ω2;设物体与卫星的质量相等,则(  )

A.F1>F2

B.a1>a2

C.v1<v2

D.ω12

答案

A、物体1和卫星2周期相等,则角速度相等,即ω12

而加速度a=rω2,则a2>a1

物体与卫星的质量相等,根据F=ma得 F2>F1.故AB错误

C、物体1和卫星2周期相等,则角速度相等,即ω12,根据v=rω,则v2>v1,故C正确,D正确

故选CD.

单项选择题

请根据下面短文回答:
Open Time: 9:00 to 17:00 Tuesdays through Sundays(sales stop at 16:00)
Ticket Prices: Full Price: RMB 30; Half Price: RMB 15
Free invitation tickets are distributed every Wednesday and shall not exceed the approved quota. The corresponding policies are:
· 200 invitation tickets are freely distributed to the public every Wednesday.
· Visitors shall go to the bamboo courtyard on the first underground floor east to pick up invitation tickets according to the order of the telephone reservation from 8:30 to 11:00 a.m. every Wednesday.
· Staff of the museum will distribute the 200 free invitation tickets based on the order of the telephone reservation until the quota is used up.
· Visitors shall get the free invitation ticket by using their valid certificate.
Distribution is limited to per person.
· Visitors using the free invitation ticket cannot visit the special exhibitions.
Tickets are only valid on the date indicated.
Year-round Free Admission Policies.
· Retired people with the provision of their certificates of retirement
· Disabled people with the provision of their certificates of disability
· Disabled soldiers with the provision of their certificates of disability
· Staff working in the culture and museum systems with the provision of their employment certificates
· Children less than 120 cm in height and accompanied by adults (those without adult accompaniment will not be admitted and the accompanying adult must purchase a ticket as per regulations)
Routes:
Subway: Muxidi Station, Line 1
Buses: No.1, No.4 and Special Bus No.1 to the stop "Muxidi".
Reservation Telephone: 63370491 63370492

The museum is open______.
[A] from Monday to Sunday
[B] from Tuesday to Sunday
[C] on Tuesday and Sunday

阅读理解

Washington, April 4----- The United States has more than 90 million families for the first time, but each contains fewer people on average than ever, the Census Bureau(统计局) reported today.

The 90,031,000 families in the United States averaged 2.64 members each as of last July 1.“The reason is, in effect, changes in the age structure,” explained Campbell Gibson, a population researcher for the bureau. Most Americans born in the great explosion of births are now in their 20’s and 30’s when they most likely to set up families, he said.

The fact that many are doing so increased the number of families from 80.4 million in 1980 t0 88.8 million in 1986 and past the 90 million mark last summer.

At the same time, the average number of people per family dropped from 2.75 in 1985 to 2.65 in 1986 and then to 2.64, Mr Gibson said.

By comparison, the 1970 Census found the average family contained 3.14 people. Families averaged more than four people in 1939 and more than five in 1880.

The growing number of ever---- smaller families is still going on, but Mr Gibson pointed out that family growth was not the same as population increase in the 1970’s.

The same age factors that are increasing the number of families also happened then, but in the 1970’s the proportion(比例) of families in each age group was also growing.

That hasn’t continued in the 1980’s for a number of possible reasons, Mr Gibson said. For example, in the 1980’s more young people have chosen to remain home with their parents instead of setting up housekeeping on their own, as many did in the 1970’s.

This could be caused by the increasing cost of housing, he said. Delays in marriage while young people go to work and school, have also been widely reported as a factor, but it was not the only factor for the family changes.

小题1:The smaller figure of families reported here is _________.

A.1980

B.80,400,000

C.2.64

D.90 million小题2:What’s the reporter’s attitude towards the present situation?

A. People should get married at later age.

  1. The average number of family members should be 2.64.
  2. It’s not clear in the report.
  3. Young people should set up housekeeping on their own, as many did in the 1970’s.
小题3:From the last paragraph we may infer that________.

A. delay in marriage will not help the number of the families

  1. delay in marriage is the major factor of the family changes
  2. the writer felt sorry that many young people now delay their marriages
  3. there must be some other factors which have led to the slower growth in the 1980’s
小题4: The underlined word “factor” in the passage means_________.

A.reason

B.something that proves be true

C.advantage

D.something that helps to bring about a result