问题 问答题

今年10月1日我国成功地发射了探月卫星“嫦娥Ⅱ号”,为我们祖国母亲的生日献上厚礼.该卫星最终定位于离月球表面高为100km的圆轨道上(可视为近月圆轨道).已知月球的质量约为地球质量的l/81,月球的半径约为地球半径的l/4,地球上的第一宇宙速度约为7.9km/s,则该探月卫星绕月运行的速率约为多少?(保留两位有效数字)

答案

第一宇宙速度为卫星绕地球在近地轨道上运动的速度,得:G

Mm
R2
=mg=m
v2
R

v=

gR
=
GM
R
=7.9km/s

同理可得,月球的第一宇宙速度为v1=

GM1
R1

v1
v
=
MR1
M1R
=
2
9
;   

   v1≈1.8km/s

答:该探月卫星绕月运行的速率约为1.8m/s.

阅读理解

C

If you have to miss a meal a day, which meal will cause you fewest health problems if you don’t eat it? If you have to make a decision of this type, most people (especially very busy people) will choose to skip breakfast.

However, many experts in the field of health consider breakfast ( the meal which “break” you “fast” ) to be the most important  meal of the day. If we eat a good breakfast, they say, we will have the energy and nutrients (营养) we need to begin our working day with vigor(活力) and stay hopeful with good honor. However, many people skip breakfast or substitute a cup of coffee for a well balanced meal. What happens if we ignore the importance of breakfast?

One recent study conducted in the United States tested a large number of people. Participants(参加者) included both males and females who ranged in age from 12 to 83. The results showed that if a person eats an adequate(丰富的) breakfast, he or she will work more efficiently(效率高地) and more productively than if he or she skips breakfast or eats a very poor breakfast. This fact appears to be especially true if a person’s work involves mental(脑力的) activities. The study showed that if school-children eat fruit, eggs, bread and milk before going to school, they will learn more quickly and will be able to concentrate on their lessons for a longer period of time than if their breakfast is inadequate(不丰富).

The study also showed that contrary to what people believe, if you skip breakfast, you will not lose weight. This is because people become so hungry if they skip breakfast that they eat too much for lunch and end up gaining weight instead of losing. So remember, if you want to lose weight, skipping breakfast will not help you. You will likely lose more weight if you decrease your other meals.

小题1: According to experts, breakfast is the most important meal of the day because _____.

A.a good breakfast breaks you down fast

B.you’ll lose weight quickly if you skip breakfast

C.breakfast provides what a person needs to work

D.after a long night, you’ll feel very hungry小题2:The underlined part “substitute a cup of coffee for a well balanced meal”(Para. 2) probably means _______.

A.to exchange a cup of coffee for a well balanced meal.

B.To drink a cup of coffee instead of a well balanced meal.

C.To change a cup of coffee into a well balanced meal.

D.To regard a cup of coffee as a well balanced meal.小题3:The example of school-children in para.3 shows that _______.

A.school-children will be quick and attentive all day if they eat breakfast

B.a proper breakfast will make mental workers more efficient

C.fruit, eggs, bread and milk are the best breakfast for mental workers

D.school-children who have breakfast are much brighter than those who don’t小题4:Which of the following is NOT true according to Para. 4?

A.Some people skip breakfast because they want to be slimmer.

B.Most people who skip breakfast actually eat more for lunch.

C.People put on weight because they eat too much breakfast.

D.Skipping breakfast won’t help people who want to lose weight.小题5:The best title of the passage is _______.

A.How to Lose Weight

B.What’s a Healthy Diet

C.Surprising Results of a Study

D.Breakfast – A Meal That Breaks You Fast

单项选择题