问题 填空题

在“研究平抛物体在的运动”的实验中,如果实验时忘记记下小球抛出点的位置,描出如图所示的轨迹,其中A为小球离开抛出点后某一时刻的位置,则可以算出小球平抛的初速度为     。抛出点的坐标为       (计算时

答案

2m/s (-20,-5)

平抛运动在水平方向上做匀速直线运动,在竖直方向上做自由落体运动,根据竖直方向上△y=gT2,求出时间间隔,再根据水平方向上的匀速直线运动求出初速度.

求出B点在竖直方向上的速度,即可求出运动的时间和b点速度,从而求出此时小球水平方向和竖直方向上的位移,即可求出抛出点的坐标.

解:(1)在竖直方向上△y=gT2,T==0.1s.则小球平抛运动的初速度v0==2m/s.

(2)A点在竖直方向上的分速度vAy==2m/s,则运动的时间t==0.2s.

水平方向上的位移x1=vt=0.4m,竖直方向上的位移y=gt2=0.2m.

所以开始做平抛运动的位置坐标x=0.2-0.4=-0.2m=-20cm,y=0.15-0.2m=-0.05m=-5cm

点评:研究平抛运动的方法是把平抛运动分解到水平方向和竖直方向去研究,水平方向做匀速直线运动,竖直方向做自由落体运动,两个方向上运动的时间相同,根据平抛运动基本公式解题,本题难度不大.

阅读理解

Imagine a boy from a small village in East Africa. He, since a very early age, has been looking after cattle. At twelve years old he knows more about cattle than most of you. However, he has never been to school. Has this boy had any education?

Education is discovering about ourselves and about the people and things around us. All the people who care about us — our parents, brothers, sisters, friends — are our teachers. In fact, we learn something from everyone we meet. We start learning on the day we were born, not on the first day we go to school. Every day we have new experiences, like finding a bird’s nest, discovering a new street in our neighborhood, making friends with someone we didn’t like before. New experiences are even more fun when we share them with other people.

Encouragement from the people around us enables us to explore things as many as possible. As we grow up, we begin to find out what we are capable of doing. You may be good at cooking, or singing or playing football. You find this out by doing these things. Just thinking about cooking doesn’t tell you whether you are good at it.

We learn so much just living from day to day. So why is school important? Of course you can learn some things better at home than at school, like how to do the shopping, and how to help old or disabled people who can’t do everything for themselves. At school, teachers help us to read and write. With their guidance, we begin to see things in different ways.

小题1: The writer takes the African boy as an example to show that _______.

A.African children are very poor.

B.some children are unlucky.

C.there are many kinds of education.

D.schools are of great importance.小题2:In the opinion of the writer,       .

A.we have to learn from the people around us.

B.the school is not important at all.

C.only people who care for us can teach us.

D.education takes place everywhere.小题3: One can find out what he / she is good at by     _.

A.what people encourage him/ her to do.

B.the teachings of those he / she meets.

C.thinking about it when growing up.

D.trying and practising things.小题4: The passage tells us that _    .

A.everyone gets education from the day he or she was born.

B.different classes of people receive different kinds of education.

C.the school is absolutely necessary if one wants to understand the world.

D.everyone will find out what he or she is good at.小题5:According to the last paragraph, we know that       .

A.the school is not so important as our living places.

B.the school enables us to understand the world in other ways.

C.the school teaches us things which are useless at home.

D.the school cannot prepare us for our daily lives.

单项选择题