问题 填空题

A、B两物体在光滑水平地面上沿一直线相向而行,A质量为5kg,速度大小为10m/s,B质量为2kg,速度大小为5m/s,它们的总动量大小为__________________kgm/s:两者碰撞后,A沿原方向运动,速度大小为4m/s,则B的速度大小为__________________m/s。

答案

40,10,

总动量P=

碰撞过程中满足动量守恒,

代入数据可得:

阅读理解

阅读理解。

     A small piece of fish each day may keep the heart doctor away. That's the finding of a study of Dutch

men in which deaths from heart disease were more than 50 percent lower among those who consumed at

least an ounce of salt water fish per day compared to those who never ate fish.

     The Dutch research is one of three human studies that give strong scientific support to the long held

belief that eating fish can provide health benefits, particularly to the heart.

     Heart disease is the number-one killer in the United States, with more than 550,000 deaths occurring

from heart attacks each year. But researchers previously have noticed that the incidence (发生率) of

heart disease is lower in cultures that consume more fish than Americans do. There are fewer heart

disease deaths, for example, among the Eskimos of Greenland, who consume about 14 ounces of fish a

day, and among the Japanese, whose daily fish consumption averages more than 3 ounces.

     For 20 years, the Dutch study followed 852 middle-aged men, 20 percent of whom ate no fish.

At the start of the study, average fish consumption was about two-thirds of an ounce each day, with more men eating lean fish than fatty fish.

     During the next two decades, 78 of the men died from heart disease. The fewest deaths were among

the group who regularly ate fish, even at levels far lower than those of the Japanese or Eskimos. This

relationship was true regardless of other factors such as age, high blood pressure, or blood cholesterol

(胆固醇) levels.

1. The passage is mainly about ________.

A. the high incidence of heart disease in some countries

B. the changes in people's diet

C. the effect of fish eating on people's health    

D. the daily fish consumption of people in different cultures

2. We can infer from the passage that there are fewer heart disease deaths ______.

A. in the countries with high consumption of fish  

B. in highly-developed countries

C. in countries of the yellow-skin race  

D. in the countries with good production of fish

3. The phrase "this relationship" in paragraph 6 refers to the connection between ______ and 

    the incidence of heart disease.

A. the amount of fish eaten

B. regular fish-eating

C. the kind of fish eaten

D. people of different areas

单项选择题