问题 填空题

在我国东北寒冷的冬季,雪橇是常见的运输工具,沿水平冰道滑行的雪橇总质量m=1200kg,雪橇与冰道之间的动摩擦因数μ=0.05.某时刻马给雪橇施加的水平拉力大小F=900N,取g=10m/s2,求:(1)雪橇受到的摩擦力大小;(2)雪橇的加速度大小.

答案

(1)雪橇受水平面得支持力为N,雪橇沿水平冰道滑行,在竖直方向平衡.

∴N=mg

根据滑动摩擦力公式:f=μN得:

f=μmg=0.05×1200×10=600N.

(2)雪橇在水平方向受拉力和摩擦力,根据牛顿第二定律得:

 F=F-f=ma  

a=

F-f
m
=
900-600
1200
m/s2=0.25m/s2  

答:(1)雪橇受到的摩擦力大小是600N;

(2)雪橇的加速度大小是0.25m/s2

阅读理解

What happens to a teenage kid when the world he thought he knew suddenly changes? Find out in Little Brother by American author Cory Doctorow. It is a fascinating book for a new generation of sci-fi readers.

Marcus Yallow, 17, from San Francisco is much more comfortable in front of a computer than obeying the rules of society. Smart, fast and wise to the ways of the networked world, he has no trouble outwitting (骗过) his high school's monitoring system. This way he and his friends get to head off to play a popular online game in real life.

While they are playing, a bomb explodes on the Bay Bridge. Marcus stops a military (军队的) vehicle to get help for his injured friend, but this simple act throws him into a Department of Homeland Security (DHS) secret prison. There he is treated as a possible terrorist(恐怖分子). He is eventually let go after four days, but his injured friend disappears.

When he returns, Marcus discovers that there are many "security measures" in place and that now all citizens are treated like potential terrorists. While some consider this government action necessary for public safety, Marcus sees this as a complete destruction of the rights he is supposed to have as a citizen.

He knows that no one will believe his story, which leaves him with only one thing to do: to take down the DHS himself. He helps organize a large network called Xnet to spread the truth, anonymously (匿名地).

The book presents a young man who is irresponsible, but learns about himself, and grows, in the course of the story. As part of this learning and growing he becomes aware of very serious issues about his society.

小题1: What kind of article does this passage belong to?     

A.A fascinating story.

B.A book review.

C.News report

D.A TV programme小题2: Marcus Yallow was sent to prison because ________.        

A.he killed his friend

B.he bombed a military vehicle

C.he did something that a possible terrorist could do

D.his injured friend disappeared小题3: From the second paragraph we can infer that _________.     

A.Marcus Yallow is much more comfortable obeying the rules of society

B.Marcus Yallow is smart, fast and wise in real life

C.Marcus Yallow always plays online games in real life

D.Marcus Yallow is expert at the network world

问答题 简答题