问题 选择题

小球从空中某处从静止开始自由下落,与水平地面碰撞后上升到空中某一高度处,此过程中小球速度随时间变化的关系如图所示,则(   )

A.在下落和上升两个过程中,小球的加速度不同

B.小球开始下落处离地面的高度为0.8m

C.整个过程中小球的位移为1.0m

D.整个过程中小球的平均速度大小为2m/s

答案

答案:B

题目分析:小球在下落和上升时,均只受重力,故加速度相同,A错误;小球在0.4s时落到地面,落地前运动的距离h==0.8m,物体下落时离地高度为0.8m,B正确;小球反弹后上升的高度(处理成反向的自由落体运动)h′==0.2m,故物体的总位移为x=0.6m,方向向下,C错误;整个过程的平均速度=1m/s,D错误。

阅读理解

阅读理解。

    All living things on the earth need other living things to live. Nothing lives alone. Most

animals must live in a group, and even a plant grows close together with others of the

same kind. Sometimes one living thing kills another, one eats and the other is eaten. Each

kind of life eats another kind of life in order to live, and together they form a food chain.

Some food chains become broken up if one of the links disappears.

    All life need sunlight to live on. But only plants can use sunlight directly. Plants are

"factories". They make food from sunlight, water and things in the soil and air. Plants feed

all other living things. Animals can only use the sun's energy after it has been changed into

food by plants. Some animals feed directly on plants, others eat smaller animals. Meat-eating

animals are only eating plants directly.

    What about human beings? We are members of many food chains. We eat wheat, rice,

vegetables. fruits and so on. We also eat meat and drink mild. But men often break up the

food chains. They kill wild animals. They also make rivers, lakes and seas dirty. When these

rivers, lakes and seas are polluted, the fish in them can not be eaten. If men eat the fish, they

will get diseases.

    Each form of life is linked to all others. Breaking the lines puts all life in danger.

1. How does every living thing on the earth live? [ ]

A. Each plant can live alone.

B. Each animal can live alone.

C. If living things want to live, they must kill each other.

D. Every living thing on the earth cannot live without others.

2. Which living things can use the sun's energy directly? [ ]

A. Animals.

B. Plants.

C. Both A and

B. D.All living things.

3. What do plants make food from? 

   They make food from _____. [ ]

A. sunlight, water and things in the soil and air

B. water, sunlight and things in the soil

C. water and things in the soil and air

D. water, sunlight and things in the soil

4. Who often break up the food chain? [ ]

A. Human beings.

B. Animals.

C. Plants and animals.

D. Men and wild animals.

5. Which of the following do you think is the best title for this passage?[ ]

A. Animals.

B. Plants.

C. Food chains.

D. Living things.

问答题 简答题