问题 选择题

虚线框abcd内的正方形区域内有竖直向下的匀强电场,如图所示.一束速率相同的氕核、氘核和氚核从a处垂直电场方向进入电场,氕核、氘核和氚核的质量分别为m、2m、3m,电荷量都为q,若其中氘核正好从c点射出,则以下判断正确的是

A.氕核从bc边射出,氚核从cd边射出

B.氕核和氚核也是从c点射出

C.氘核和氚核在电场中的运动时间相同,大于氕核在电场中的运动时间

D.氕核在电场中的运动时间最短,氚核在电场中的运动时间最长

答案

答案:C

题目分析:氕核、氘核和氚核三个粒子的电量相等,都带正电荷,质量不等,在电场中只受到电场力作用,粒子在竖直方向上做匀加速直线运动,在水平方向上做匀速直线运动,根据牛顿运动定律分析

因为三个粒子的电量相等,所以可得受到的电场力相等,根据牛顿第二定律可得,故氕核从cd边射出,氚核从bc边射出,AB错误,

因为氚核和氘核在水平方向上的位移相等,即,所以两者的运动时间相等,又因为氕核的水平位移小于,所以氕核在电场中的运动时间最短,C正确,D正确

点评:做此类问题,首先弄明白带电粒子在各个方向上的运动性质,然后结合牛顿第二定律分析加速度的大小,再根据水平方向上的位移判断时间,

完形填空
Are people less happy or more happy the older they get? If you answered more happy, then you were right, based on a study published two years ago. It found that people generally become happier and experience less worry after age fifty. In fact, it found that by the age of eighty-five, people are happier with their life than they were at eighteen.
The findings came from a Gallup survey of more than three hundred forty thousand adults in the United States in 2008. At that time, the people were between the ages of eighteen and eighty-five.
Arthur Stone in the Department of Psychiatry and Behavioral Science at Stony Brook University in New York led the study. His team found that levels of stress were highest among adults between the ages of 22 and 25. Stress levels dropped sharply after people reached their fifties.
Happiness was highest among the youngest adults and those in their early seventies. But the people least likely to report negative emotions were those in their seventies and eighties.
The survey also found that men and women have similar emotional patterns as they grow older. However, women at all ages reported more sadness, stress and worry than men did.
The researchers also considered possible influence like having young children, being unemployed or being single. But they found that influences like these did not affect the levels of happiness and well-being related to age.
So why would happiness increase with age? One theory is that, as people get older, they become more thankful for all that they have and have better control of their emotions. They also spend less time thinking about bad experiences.
Happiness is not the only thing that apparently improves with age. In a study published this year, people in their eighties reported the fewest problems with the quality of their sleep.
Researchers surveyed more than 150,000 American adults. The study, led by Michael Grander at the University of Pennsylvania, appeared in the journal Sleep.
The original goal was to confirm the popular belief that aging is connected with increased sleep problems. The survey did find an increase during middle age, especially in women. But except for that, people reported that they felt their sleep quality improved as they got older.
Title
The older you get, the 小题1:________ you are!
小题2:_____ of a Gallup survey
People are happier with their life when they are at 85 than they are at 18. Happiness is highest among the youngest adults and those in their early seventies.
People in their seventies and eighties are 小题3:______ likely to report negative emotions.
Men and women have similar emotional patterns as they grow older, 小题4:____ that women always report more sadness, stress and worry.
小题5:______ for this phenomenon
People become more thankful for 小题6:_____ they have.
People can 小题7:____ their emotions better.
People spend less time thinking about bad experiences.
Effects of aging 小题8:_____ sleep
On the one hand, sleep problems 小题9:_____ during middle age.
On the other 小题10:____, sleep quality improves as people get older.
问答题 简答题