问题 计算题

如图所示,静置于水平地面的三辆手推车沿一直线排列,质量均为m,人在极短的时间内给第一辆车一水平冲量使其运动,当车运动了距离L时与第二辆车相碰,两车以共同速度继续运动了距离L时与第三车相碰,三车以共同速度又运动了距离L时停止。车运动时受到的摩擦阻力恒为车所受重力的k倍,重力加速度为g,若车与车之间仅在碰撞时发生相互作用,碰撞时间很短,忽略空气阻力,求:

(1)整个过程中摩擦阻力所做的总功;

(2)人给第一辆车水平冲量的大小;

答案

(1)(2)

题目分析:(1)

(2),   , 

点评:本题关键在于运动的过程较多,有三个匀减速过程和两个碰撞过程,可以交叉运用动能定理和动量守恒定律列式求解,题中涉及的字母较多,要有足够的耐心,更要细心!

单项选择题 A1/A2型题
阅读理解

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 plants. Flowering

plants can make seeds. 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 (胚芽).

Spores are 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 are all on wet and shady places, they usually grow into new

plants.

1. The main idea of the first paragraph is that _____. [ ]

A. plants are important for life

B. plants cannot grow without air

C. there are many plants in the world

D. we can not live without water

2. Plants can make food from _____. [ ]

A. flower, water and air

B. water, sunlight and air

C. air, water and soil

D. air, sun and light

3. What can we infer (推断) from the passage? [ ]

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

4. This passage may be taken from _____. [ ]

A. a medicine book

B. a novel

C. a science magazine

D. an experiment report