问题 多选题

关于质点,下列说法中正确的是(  )

A.只要体积小就可以视为质点

B.若物体的大小和形状对于所研究的问题属于无关或次要因素时,可把物体当作质点

C.质点是一个理想化模型,实际上并不存在

D.因为质点没有大小,所以与几何中的点是一样的

答案

A、原子核很小,但在研究原子核内部的结构等的时候是不能看成质点的,所以A错误.

B、若物体的大小和形状对于所研究的问题属于无关或次要因素时,我们就可把物体当作质点,故B正确;

C、质点是忽略了物体的形状和大小,把物体看成一个具有质量的点,这是为了研究问题方便而建立的理想化模型,实际不存在,所以C正确;

D、质点没有大小但是有质量,几何中的点没有质量,故不一样,故D错误.

故选BC.

阅读理解

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

Why Exercise Is Cool?

1. Exercise Strengthens Muscles

Did you ever do a push-up or swing across the monkey bars at the playground?    小题1:   By using your muscles to do powerful things, you can make them stronger. For older teens and adults, this kind of workout can make muscles bigger, too.

2.    小题2: 

Can you touch your toes easily without yelling ouch? Most kids are pretty flexible, which means that they can bend and stretch their bodies without much trouble. Being flexible is having “full range of motion,” which means you can move your arms and legs freely without feeling tightness or pain.

3. Exercise Keeps the Balance

   小题3:  Your body needs a certain amount of calories every day just to function, breathe, walk around, and do all the basic stuff.    小题4:   If you’re not very active, your body won’t need as many calories.

Whatever your calorie need is, if you eat enough to meet that need, your body weight will stay about the same. If you eat more calories than your body needs, it may be stored as extra fat.

4. Exercise Makes You Feel Good

It feels good to have a strong, flexible body that can do all the activities you enjoy—like running, jumping, and playing with your friends. It’s also fun to be good at something, like scoring a basket, hitting a home run, or perfecting a dive.

But you may not know that exercising can actually put you in a better mood.    小题5:   It’s just another reason why exercise is cool!

A.So you want to do some aerobic (有氧的) exercise right now?

B.Food gives your body fuel in the form of calories, which are a kind of energy.

C.When you exercise, your brain releases a chemical, which may make you feel happier.

D.Those are exercises that can build strength.E. Exercise Makes You Flexible

F. Exercise Makes Your Heart Happy

G. But if you’re active, your body needs an extra measure of calories or energy.

问答题 简答题