问题 填空题

(1)在“用单摆测重力加速度”的实验中,下列措施中可以提高实验精度的是______.

A.选细线做为摆线

B.单摆摆动时保持摆线在同一竖直平面内

C.拴好摆球后,令其自然下垂时测量摆长

D.计时起止时刻,选在最大摆角处

(2)某同学在做“利用单摆测重力加速度”的实验中,先测得摆线长为97.50cm,摆球直径为2.00cm,然后用秒表记录了单摆振动50次所用的时间,则:

①该摆摆长为______ cm.

②如果测得的g值偏小,可能的原因是______.

A.测摆线长时摆线拉得过紧

B.摆线上端悬点末固定,振动中出现松动,使摆线长度增加了

C.开始计时时,秒表过迟按下

D.实验中误将49次全振动记为50次

③为了提高实验精度,在实验中可改变几次摆长l并测出相应的周期T,从而得出一组对应的l与T的数据,再以l为横坐标,T2为纵坐标,将所得数据连成直线如图所示,并求得该直线的斜率为k,则重力加速度g=______(用k表示).

答案

(1)为了提高测量的精确度,摆线应选用细线,单摆在同一个竖直面内摆动,防止出现圆锥摆,测量摆长时应在摆球自然下垂时测量,从平衡位置(最低点)开始计时,因为速度最大,误差比较小.故ABC正确,D错误.

(2)①摆长l=97.50+1cm=98.50cm.

②A、根据g=

4π2l
T2
知,测摆线长时摆线拉得过紧,导致摆长偏大,重力加速度偏大.故A错误.

  B、摆线上端悬点末固定,振动中出现松动,使摆线长度增加了,摆动的过程中,摆长变短,根据g=

4π2l
T2
知,重力加速度偏小.故B正确.

   C、开始计时时,秒表过迟按下,导致周期变小,根据g=

4π2l
T2
知,重力加速度偏大.故C错误.

D、实验中误将49次全振动记为50次,导致周期变小,根据g=

4π2l
T2
知,重力加速度偏大.故D错误.

故选B.

③根据g=

4π2l
T2
,知T2=
4π2l
g
,图线的斜率k=
4π2
g
.所以g=
4π2
k

故答案为:(1)ABC (2)98.50,B,

4π2
k

单项选择题
阅读理解

Farah was sitting in the kitchen going over the party list with her mother.The exams were over and Farah wanted to invite her friends for a party.

“Farah,aren’t you going to invite Hafsa?”her mother asked.Hafsa had been her best friend since childhood.

“Mother,you know I am now a part of Purple Girls Club and we have some rules about people we can be friends with,”Farah answered.

“Really?And what are the rules?”her mother asked.

“Well,only very pretty girls can be part of our group.And Hafsa is so...you know...dark.”

“I cannot believe it,”her mother said angrily. 

As Farah left the kitchen,her father called  her from the living room.

Farah went to her father and paled when she saw the exam report in his hands.“Farah,what has happened to your grades?You have failed in Mathematics,”her father said.

Farah had no answer.The truth was that the activities of Purple Girls Club left her with very little time for studies.

“Farah,it says that you can take part in supplementary exams(补考).If your grades don’t improve then,I’ll cancel(取消) your trip to Spain.”

Farah went to her room and called Gina,the leader of Purple Girls Club, “Gina,can you help me to complete my notes before the exams?”

Gina laughed.“Exams?Who cares about exams?”

One by one,she called her friends in the club but no one seemed to care or wanted to help.

Farah knew Hafsa would help her.Farah also knew Hafsa had been hurt by her,but Hafsa said,“If you need any help,just let me know.We can study together till your exams.”

Next Monday,as two friends entered the school together,Gina called out.

“Farah,you know our rules.You cannot be friends with those who do not belong to our club.”

“Gina,I have a new rule about friendship,”Farah replied.

小题1:After Farah became a member of Purple Girls  Club,she chose a friend according to a person’s________.

A.looks

B.usual activities

C.grades

D.favorite colors小题2:Farah became pale after going to her father because________.

A.he didn’t allow her to go to Spain

B.she didn’t do well in her exams

C.she had to leave Purple Girls Club

D.he asked her to improve her grades小题3:Which word can best describe Hafsa?

A.Silly.

B.Beautiful.

C.Rude.

D.Kind.小题4:What lesson can we learn from the passage?

A.A friend in need is a friend indeed.

B.A perfect friend will never be found.

C.Be slow in choosing a friend.

D.Friendship can be developed easily.