问题 选择题

如图所示,一汽车通过拱形桥顶点时的速率是v、汽车对拱形桥压力是车重的

3
4
.如果要使汽车通过桥顶时对桥恰好没有压力,则车速(  )

A.应恰好为零,车静止在桥的顶点

B.应为原来的4倍

C.应为原来的2倍

D.应为原来的

2倍

答案

根据牛顿第二定律有:mg-N=m

v2
R
,N=
3
4
mg
,解得v=
gR
4

当车对桥顶无压力时,有:mg=m

v2
R
,解得v′=
gR
,知v′=2v.故C正确,A、B、D错误.

故选C.

完形填空

One day I was doing an experiment in front of the classroom, wearing my favorite shirt. A voice came, “Nice shirt”. Then another   1  said, “That shirt belonged to my dad. Jimmy’s mother works for my family. We meant to throw the shirt away, but gave   2   to her instead.” Hearing the words, I was embarrassed. It was Mike. Mom worked for his family.

In the evening, I told my mom what had happened. She was silent for a while and then called her employer, “I will   3  work for your family.” That night, she knew her life’s   4   was something greater. She decided to find a more meaningful job.

The next day she   5   with the headmaster of a local public school. She was told that she could not teach without a proper education. So Mom decided to   6  a university.

A year later, she went back to the headmaster. He said, “You are serious, aren’t you? I think I have a   7   for you as a teacher’s assistant. This opportunity deals with some mentally disabled children with little or   8  chance of learning.” Mom accepted the opportunity very   9  .

For almost three years, she saw many teachers give up on the children and   0  , feeling   upset. Then one day, the headmaster   11   in her classroom, saying, “We have watched how you  12   the children over the last three years and admire your hard-working spirit. We all agree that you should be the   13  of this class.”

My mom spent over 20 years there. I was proud of her   14  she never gave up and also showed me how to deal with   15   situations. During her career, she was chosen as “Teacher of the Year”.

小题1:

A.shout

B.noise

C.sound

D.voice小题2:

A.it

B.them

C.one

D.this小题3:

A.even so

B.in reality

C.no longer

D.more than小题4:

A.goal

B.trick

C.problem

D.routine小题5:

A.ran

B.met

C.stayed

D.worked小题6:

A.visit

B.design

C.attend

D.start小题7:

A.condition

B.function

C.promotion

D.position小题8:

A.no

B.much

C.big

D.great小题9:

A.angrily

B.bitterly

C.eagerly

D.strangely小题10:

A.come

B.leave

C.return

D.succeed小题11:

A.went up

B.took up

C.handed up

D.turned up小题12:

A.accuse

B.blame

C.treat

D.cheat小题13:

A.monitor

B.teacher

C.headmaster

D.librarian小题14:

A.because

B.once

C.unless

D.if小题15:

A.pleasing

B.challenging

C.exciting

D.amazing

问答题 简答题