问题 实验题

图中为“验证牛顿第二定律”的实验装置示意图。盘和重物的总质量为m,小车和砝码的总质量为M。实验中用盘和重物总重力的大小作为细线对小车拉力的大小。

①实验中,为了使细线对小车的拉力等于小车所受的合外力,先调节长木板一端定滑轮的高度,使细线与长木板平行。接下来还需要进行的一项操作是     (填写所选选项的序号)。

A.将长木板水平放置,让小车连着已经穿过打点计时器的纸带,给打点计时器通电,调节m的大小,使小车在盘和重物的牵引下运动,从打出的纸带判断小车是否做匀速运动。

B.将长木板的右端垫起适当的高度,让小车连着已经穿过打点计时器的纸带,撤去盘和重物,给打点计时器通电,轻推小车,从打出的纸带判断小车是否做匀速运动。

C.将长木板的右端垫起适当的高度,撤去纸带以及盘和重物,轻推小车,观察判断小车是否做匀速运动。

②实验中要进行质量m和M的选取,以下最合理的一组是     

A.M=20g,m=10g、15g、20g、25g、30g、40g

B.M=200g,m=20g、40g、60g、80g、100g、120g

C.M=400g,m =10g、15g、20g、25g、30g、40g

D.M=400g,m ="20" g、40g、60g、80g、100g、120g

③图中是实验中得到的一条纸带,A、B、C、D、E、F、G为7个相邻的计数点,量出相邻的计数点之间的距离分别为x1、x2、x3、x4、x5、x6。已知相邻的计数点之间的时间间隔为T,关于小车的加速度a的计算方法,产生误差较小的算法是    

A.

B.

C.

D.

答案

 ①B  ②C  ③D

题目分析:①平衡摩擦力既要平衡纸带和打点计时器之间的摩擦,还有平衡小车和木板之间的摩擦,所以平衡摩擦力时一定要连上纸带,在没有拉力作用下若能匀速直线运动,说明摩擦力已经平衡,要保证没有拉力,就要去除盘和重物。②实验设计中以砝码和盘的重力作为小车合力,事实上,小车和砝码盘一起运动,加速度,绳子拉力即小车合力,只有当时,绳子拉力才近似等于砝码和盘的重力,对照选项符合只有选项C。③根据,纸带数据给出6个连续的间距,任意两个都可以计算出加速度,但是不够准确,有误差,所以选择六个数据都用上,,整理可得,选项D对。

阅读理解

阅读理解。

     Kelly Reeves was getting ready for a trip when her phone slipped into a sink full of water.

Panic moment! She quickly picked up the wet phone and tried to turn it on, but nothing worked.

Her first reaction? She got dressed, drove to the nearest store, and bought a new model at full price.    

     A new study finds that fear of losing your phone is a common illness. About 66 percent of those

surveyed suffer from nomophobia or "no mobile phone phobia". Interestingly, more women worry

about losing their phone than men.    

     Fortunately, there's a solution.    

     The first step is to figure out if you have nomophobia. Checking your phone too often is one thing,

but the true sign of a problem is that you can't conduct business or go about your routine when the fear

becomes so severe.    

     Do you go to unusual lengths to make sure you have your phone? That's another sign of a problem.

If you find you check your phone plenty of times per hour, or a total of an hour per day, there may be

a problem.    

     Some of the treatments are similar to those for treating anxiety attacks: Leaving the phone behind

and not checking e-mail or text messages, and then learning to tolerate the after anxiety. Even if this

leads to a high level of worry and stress, the solution is to push through the fear and learn to deal with

not having your phone.    

     Of course, there are also technological alternatives. Luis Levy, a co-founder at Novy PR, says he

uses an application called Cerberus that can automatically track the location of his phone. To find it, he

can just go to a Web site and see the phone's location.    

     He also insures his phone through a service called Asurion. The company's description of its product

reads like a prescription for anxiety: "60 million phones are lost, stolen or damaged each year. You'll

have complete peace of mind knowing that your phone is protected and you can quickly reconnect

with family,friends and work, as soon as the very next day!"

1. Why does the author mention Kelly's experience in the first paragraph?

A. To introduce the topic for discussion.

B. To inform us that mobile phones are useful.

C. To warn us that we should be careful.

D. To tell us we should get phones ready for a trip.

2. The underlined word "nomophobia" in Paragraph 2 means ________.

A. Habits of using mobile phones.

B. Fear of losing mobile phones.

C. Eagerness for new mobile phones.

D. Independence of mobile phones.

3. Which of the following is a way to treat nomophobia?

A. Avoiding using phone for some time

B. Learning more about modern technology.

C. Protecting one's phone against any damage.

D. Not using a mobile phone in one's daily work.

4. Why can the service called Asurion help to treat nomophobia?

A. It lets you know other people also lose their phones.

B. It will give you a new phone through insurance.

C. It enables you to reconnect with your acquaintance.

D. It gives you a prescription to treat nomophobia.

5. What is the passage mainly about?

A. Attitude toward mobile phone.

B. New mobile phone technology.

C. Disadvantages of mobile phone.

D. Solutions to nomophobia

单项选择题