问题 问答题

汽车正以15m/s的速度行驶,驾驶员突然发现前方有障碍,便立即刹车.假设汽车刹车后做加速度大小为5m/s2的匀减速运动.求刹车后4秒内汽车滑行的距离.

答案

由题意知v0=15m/s,a=-5m/s2,求汽车4s内的位移:

根据v=v0+at,得当汽车速度减为0时所需时间t=

0-15
-5
s=3s,即汽车运动3s后停止运动,故求汽车4s内的位移,即为汽车3s内的位移:

x=v0t+

1
2
at2得位移x=15×3+
1
2
×(-5)×32m=22.5m

答:刹车后4秒同汽车滑行的距离为22.5m.

单项选择题

Passage Two

If there is one thing I’m sure about, it is that in a hundred years from now we will still be reading newspapers. It is not that newspapers are a necessity. Even now some people get most of their news from television or radio. Many buy a paper only on Saturday or Sunday. But for most people reading a newspaper has become a habit passed down from generation to generation.

The nature of what is news may change. What basically makes news is what affects our lives—the big political stories, the coverage of the wars, earthquakes and other disasters, will continue much the same. I think there will be more coverage of scientific research, though. It’s already happening in areas that may directly affect our lives, like genetic engineering. In the future, I think there will be more coverage of scientific explanations of why we feel as we do—as we develop a better understanding of how the brain operates and what our feelings really are.

It’s quite possible that in the next century newspapers will be transmitted electronically from Fleet Street and printed out in our own home. In fact, I’m pretty sure that how it will happen in the future. You will probably be able to choose from a menu, making up your own newspaper by picking out the things you want to read--sports and international news, etc.

I think people have got it wrong when they talk about competition between the different media. They actually feed off each other. Some people once foresaw that television would kill off newspapers, but that hasn’t happened. What is read on the printed page lasts longer than pictures on a screen or sound lost in the air. And as for the Internet, it’s never really pleasant to read something just on a screen.

What will probably be on in the newspaper made by yourself()

A. Sports and international news.    

B. A menu of important news. 

C.The most important news.     

D.What you are interested in.

问答题 简答题