问题 问答题

某同学利用打点计时器测量小车做匀变速直线运动的加速度.

①电磁打点计时器是一种使用______(填“交流”或“直流”)电源的计时仪器,它的工作电压是4-6V,当电源的频率为50Hz时,它每隔______s打一次点.

②使用打点计时器时,接通电源与让纸带随小车开始运动这两个操作过程的操作顺序,应该是______

A.先接通电源,后释放纸带B.先释放纸带,后接通电源

C.释放纸带的同时接通电源D.哪个先,哪个后都可以

③实验中该同学从打出的若干纸带中选取一条纸带,如下图所示,纸带上按时间顺序取为A、B、C、D四个计数点,每两个点之间还有四个点未画出.用尺子测得各点的距离为s1=3.62cm,s2=4.75cm,s3=5.88cm.根据纸带数据可以判断小车在做匀加速直线运动,理由是______(请用文字描述);在记数点C所代表的时刻,纸带运动的瞬时速度是______m/s;小车的加速度是______m/s2.(以上两空小数点后保留两位数字)

答案

(1)电磁打点计时器使用交流电源,频率为50Hz,则每隔0.02s打一个点.

(2)使用打点计时器是,应先接通电源,再释放纸带.故选A.

(3)因为小车在相邻相等时间内的位移之差相等s3-s2=s2-s1,所以小车做匀加速直线运动.

C点的速度等于BD段的平均速度,则vC=

s2+s3
2T
=
(4.75+5.88)×10-2
0.2
m/s=0.53m/s.

根据△x=aT2得,a=

△x
T2
=
1.13×10-2
0.01
m/s2=1.13m/s2

故答案为:(1)①交流,0.02;②A;③相邻相等时间间隔内的位移差相等; 0.53,1.13

阅读理解

阅读理解。

     If you go into the forest with friends, stay with them. If you don't, you may get lost (迷路) , this is

what you should do. Sit down and stay where you are. Don't try to find your friends let them find you

instead. You can help them find you by staying in one place. There is another way to help your friends or

other people to find you. You can shout or whistle (吹口哨) three times. Stop. Then shout or whistle

three times again. Any signal (信号) given three times is a call for help.

     Keep on shouting or whistling. Always three times together. When people hear you, they will know

that you are not just making a noise for fun. They will let you know that they have heard your signal.

They will give you two shouts or two whistles. When a signal is given twice,  it is an answer to a call for

help.

     If you don't think that you will get help before night comes , try to make a little house with branches

(树枝) . Make yourself a bed with leaves (树叶) and grass.

     When you need some water, you have to leave your little branch house to look for it. Don't just walk

away. Pick off small branches and drop (扔下) them as you walk in order to (为了) go back again easily. When you are lost, the most important thing to do is to stay in one place.

1. If you get lost in the forest, you should _             .

A. try to find your friends

B. stay in one place and give signals

C. walk around the forest

D. shout as Loudly as possible

2. Which signal is a call for help?

A. Shouting here and there.

B. Crying twice.

C. Shouting or whistling three times together.

D. Whistling everywhere in the forest.

3. When you hear two shouts or two whistles, you know that               .

A. someone is afraid of an animal

B. people will come to help you

C. someone needs help

D. something terrible will happen

4. What's the meaning of the underlined sentence?

A. Leave branches to find your way back.

B. Pick off  branches to build another house.

C. Use branches to make a bed.

D. Drop branches to look for water.

5. The main (主要的) idea of the passage is _______.

A. how to travel in the forest

B. how to spend the night in the forest

C. what you should do if you want to get some water

D what you should do if you are lost in the forest

单项选择题 A1/A2型题