问题 计算题

(12分)汽车从静止开始作匀加速直线运动,经5s后速度达到 10m/s,然后匀速运动了 20s,接着以5m/s2的加速度减速, 则

(1)汽车在加速阶段的加速度是多少?

(2)在第 28s末的速度大小是多少?

(3)汽车全程的路程是多大?

答案

⑴2m/s2 ⑵ 0(3)235m

题目分析:(1)匀加速直线运动阶段的加速度为

(2)第28s末时,汽车正做匀减速直线运动,并且减速了3s,而汽车需要静止的时间为,所以减速第三秒时,汽车处于静止

(3)匀加速阶段的位移为

匀速阶段的位移为

匀减速阶段的位移为

故全程的位移为

单项选择题

For some people, the light of human attention has an unbearable brilliance. Like ivy along the dim edge of a garden, they prefer the social shadows, shunning parties, publicity and fame of any sort. Then there are the flowers of the human arboretum. For them, being in the view of others seems necessary for life itself. From Hollywood to fabricated prime-time reality, this spotlight-dependent species is thriving.
But what about the individuals who crave attention for more desperate reasons Those who resort to unusual ways to get it Lately, it seems, a dark bloom of these characters has emerged. For motives known only to themselves, they have won notoriety by drawing on an almost sacred well of social status: victim hood.
In early April, US national news outlets tracked the disappearance of Audrey Seiler, a sophomore at the University of Wisconsin in Madison. Police and hundreds of concerned citizens searched for four days before Seiler was discovered. Seiler said she was kidnapped. Within hours, however, her story fell apart. Police announced that her abduction had been a hoax. Why would a popular student make herself disappear Her motive remains a mystery, but perhaps it had something to do with the search parties and the news bulletins that surrounded her.
Sympathy is a powerful sentiment that can connect complete strangers. But if it’s used to manipulate, the backlash can be much more intense.
In February, a Waterbury, Connecticut, man was arrested as a result of exploiting sympathy. Edward Valentin told reporters that he had received word that his wife, serving in Iraq, had been killed in an explosion. Police said Valentin admitted the fabrication, reasoning that if people felt sorry for him maybe the military would send his wife home. Evidence, however, points elsewhere.
In its extreme form, such a craving shows up in mental disorders, where sufferers may seek attention by causing themselves harm. But even when it comes with no diagnosis, a deep craving to be noticed can have a wide impact.
For these individuals, victim hood represents a "pure state of guilt-free entitlement," said psychologist Richard Levak, of Del Mar, California. "They go from being utterly deprived to being utterly indulged. In today’s world ... people have become more depressed and disconnected from each other. So you get people who crave affection and attention and approval. They don’t know how to ask for it and they don’t know how to get it. That leaves them vulnerable," Levak said.

Edward Valentin made up the story in order to ______.

A.get his wife back home from Iraq

B.make people feel sorry for him

C.express deep love for his wife

D.draw attention to himself

选择题