问题 实验题

(1)一打点计时器固定在斜面上某处,一小车拖着穿过打点计时器的纸带从斜面上滑下,如图1所示。图2是打出的纸带的一段。

①已知打点计时器使用的交流电频率为50Hz,利用图2给出的数据可求出小车下滑的加速度a=_________。

②为了求出小车在下滑过程中所受的阻力,还需测量小车质量m、斜面上两点间距离l及这两点的高度差h。用测得的量及加速度a和重力加速度g表示小车在下滑过程中所受的阻力计算式为f =             

(2)在做“探究动能定理”的实验中,小车的质量为m,使用橡皮筋6根,每次增加一根,实验中W、v、v2的数据已填

在下面表格中,试在图中作出图象,实验结论是:                    .

Wv/(m/s)v2/(m2/s2)
000
1.000.800.64
2.001.101.21
3.001.281.64
4.001.532.34
5.001.763.10
6.001.893.57
.

答案

(1)①4.00m/s2(3.90~4.10 m/s2之间都正确)  ②

(2)图像见解析。

实验结论:在误差范围内,合外力做的功和速率的平方成正比。(或者:在误差范围内,合外力做的功等于动能的增加量)

题目分析:(1)①可求得相邻相等时间内的位移之差的平均值为0.64cm,根据)解得a=4.00m/s2;②根据牛顿定律,其中,解得f=;(2)图线如下图;实验结论:在误差范围内,合外力做的功和速率的平方成正比。(或者:在误差范围内,合外力做的功等于动能的增加量)

 

选择题
单项选择题

Few people would defend the Victorian attitude to children, but if you were a parent in those days, at least you knew where you stood: children were to be seen and not heard. Freud and his company did away with all that and parents have been bewildered ever since. The child’s happiness is all-important, the psychologists say, but what about the parents’ happiness Parents suffer continually from fear and guilt while their children gaily romp about pulling the place apart. A good "old-fashioned" spanking is out of the question: no modern child-rearing manual would permit such barbarity. The trouble is you are not allowed even to shout. Who knows what deep psychological wounds you might inflict The poor child may never recover from the dreadful traumatic experience. So it is that parents bend over backwards to avoid giving their children complexes which a hundred years ago hadn’t even been heard of. Certainly a child needs love, and a lot of it. But the excessive permissiveness of modern parents is surely doing more harm than good.

Psychologists have succeeded in undermining parents’ confidence in their own authority. And it hasn’t taken children long to get wind of the fact. In addition to the great modern classics on child-care, there are countless articles in magazines and newspapers. With so much unsolicited advice flying about, mum and dad just don’t know what to do any more. In the end, they do nothing at all. So, from early childhood, the kids are in charge and parents’ lives are regulated according to the needs of their offspring. When the little dears develop into teenagers, they take complete control. Lax authority over the years makes adolescent rebellion against parents all the more violent. If the young people are going to have a party, for instance, parents are asked to leave the house. Their presence merely spoils the fun. What else can the poor parents do but obey

Children are hardy creatures (far hardier than the psychologists would have us believe) and most of them survive the harmful influence of extreme permissiveness which is the normal condition in the modern household. But a great many do not. The spread of juvenile delinquency in our own age is largely due to parental laxity. Mother, believing that little Johnny can look after himself, is not at home when he returns from school, so little Johnny roams the streets. The dividing-line between permissiveness and sheer negligence is very fine indeed.

The psychologists have much to answer for. They should keep their mouths shut and let parents get on with the job. And if children are knocked about a little bit in the process, it may not really matter too much. At least this will help them to develop vigorous views of their own and give them something positive to react against. Perhaps there’s some truth in the idea that children who have had a surfeit of happiness in .their childhood appear like stodgy puddings and fail .to make a success of life.

What does the author wants to illustrate with Johnny roaming the streets()

A. An instance of arbitrariness

B. A consequence of permissiveness

C. A prototype of classics

D. An example of irresponsibility