问题 填空题

在水平线上有17个质点,每相邻两质点间的水平距离均为4cm,如图所示.有一简谐波在水平方向传播,已知第5个质点完成一次全振动经过的路程是 8cm,时间为2S.当它从平衡位置开始向上振动经过12cm路程时,第17个质点即将振动,则该波的传播速度是______m/s,在图中画出第17个质点即将振动时的波形图.

答案

(1)由题知,波从第5个质点传播到第17个质点所用的时间为t=1.5T=3s

第5、17质点间的距离x=(17-5)×4×10-2 m=0.48m

波速v=

x
t
=0.16m/s  

(2)如图14所示,

故答案为:0.16;如上图.

阅读理解

Plants are very important living things. Life could not go on if there were no plants. This is because plants can make food from air, water and sunlight. Animals and man cannot make food from air, water and sunlight. Animals get their food by eating plants and other animals. Therefore animals and man need plants in order to live. This is why we find that there are so many plants around us.

If you look carefully at the plants around you, you will find that there are two kinds of plants: flowering plants and non-flowering(不开花的) plants.

Flowering plants can make seeds(种子). The seeds are protected by the fruits. Some fruits have one seed, some have two, three or four, and some have many seeds. But a few fruits have no seeds at all. An example of a fruit without seeds is the banana fruit.

Most non-flowering plants do not grow from seeds. They grow from spores(孢子). Spores are very, very small. Some spores are so small and light that they can float in the air. We may say that spores are quite the same as seeds. When these spores fall on wet and shady(阴凉的) places, they usually grow into new plants.

小题1:What fact does the passage lead you to believe?

A.Of all living things, animals are most important.

B.Spores are seeds.

C.All fruits of flowering plants have seeds.

D.Without plants, man will die out.小题2:The paragraph following the passage will be about ________.

A.how plants can make food from air

B.how spores grow into new plants

C.why some plants have no seeds

D.why non-flowering plants are more important than flowering plants小题3:This passage is most likely to be taken from ________.

A.a story book

B.a novel

C.a science magazine

D.a laboratory report

单项选择题