题目内容

【题目】如图所示，A、B两球质量相等，光滑斜面的倾角为，图甲中，A、B两球用轻弹簧相连，图乙中A、B两球用轻质杆相连，系统静止时，挡板C与斜面垂直，弹簧、轻杆均与斜面平行，则在突然撤去挡板的瞬间有（ ）

A．两图中两球的加速度均为

B．两图中A球的加速度均为零

C．图乙中轻杆的作用力一定不为零

D．图甲中B球的加速度是图乙中B球加速度的2倍

【答案】D

【解析】当撤去挡板时，甲图中由于弹簧的压缩量不能突变，A球还会受到不变的弹力作用，能继续平衡；而B球沿斜面方向受到重力分力mgsin和弹簧弹力mgsin两个力，所以B球会产生2gsin加速度。乙图中轻杆的形变很小，撤掉挡板后，轻杆的弹力可以发生突变。将A、B看成整体可知，A、B会沿斜面以gsin加速度下滑，可知轻杆的弹力瞬间消失。综上所述，选项D正确。

练习册系列答案
相关题目

【题目】A

In 1995, Oseola McCarty gave a present of $ 150,000 to the University of Southern Mississippi. She wanted to help poor students. It was a very generous thing to do. But her friends and neighbors were surprised. McCarty was a good woman. She went to church. She was always friendly and helpful. But everyone in her town knew that McCarty was not rich. In fact, she was poor.

How did a poor 86-year-old woman have so much money? Oseola McCarty was born in 1908 in Hattiesburg, Mississippi. She had to leave school when she was eight years old to help her family. She took a job washing clothes. She earned only a few dollars a day. Oseola washed the clothes by hand. Then she hung the clothes to dry. She did this for nearly 80 years. In the 1960s’ she bought an automatic washer and dryer. But she gave them away. She did not think they got the clothes clean enough! At that time, many people started to buy their own washers and dryers. McCarty did not have much work, so she started to iron clothes instead.

McCarty never married or had children. Her life was very simple. She went to work and to church. She read her Bible. She had a black-and-white television. But she did not watch it very much. It had only one channel.

McCarty saved money all her life and eventually had about $250,000.When she was 86, a lawyer helped her make a will. She left money to the church, her relatives, and the university. McCarty just wanted to help others. She did not think she was a special person. But then people found out about her present to the university. She received many honors(荣誉). She even flew in an airplane for the first time! Oseola McCarty died in 1999.She was a shy and ordinary woman who became famous.

【1】Oseola McCarty gave $150,000 to the University of Southern Mississippi __________.

A. to help the poor students

B. to surprise her friends and neighbors

C. to show her generosity

D. to be a good and rich woman

【2】From the story we know ___________.

A. McCarty was born in a poor family near the University of Southern Mississippi

B. everyone was surprised because they thought McCarty had no education

C. washers and dryers brought a change in McCarty’s life

D. McCarty gave half of her money to the church and her relatives.

【3】 Which of the following is true?

A. McCarty had to work to help her family after school every day.

B. McCarty learned to read the Bible by herself in the school.

C. McCarty made one third of her money by washing and ironing clothes.

D. McCarty did not have her own family because she had no husband or children.

【4】 From which of the following can we tell McCarty lived a simple life?

A. She worked hard all her life.

B. She didn’t think she was special.

C. She didn’t have many interests.

D. She had a TV set with many channels.

【题目】目前有些居民区内楼道灯的控制，使用的是一种延时开关。该延时开关的简化原理如图所示。图中D是红色发光二极管（只要有很小的电流通过就能使其发出红色亮光），R为限流电阻，K为按钮式开关，虚线框内S表示延时开关电路，当按下K接通电路瞬间，延时开关触发，相当于S闭合，这时释放K后，延时开关S约在1 min后断开，电灯熄灭。根据上述信息和原理图，我们可推断：

按钮开关K按下前，发光二极管是________（填“发光的”或“熄灭的”），按钮开关K按下再释放后，电灯L发光持续时间约________min。这一过程中发光二极管是________。限流电阻R的阻值和灯丝电阻RL相比，应满足R________RL的条件。

【题目】如图所示，可看做质点的两物块A，B，质量分别为2m，m。A放在光滑水平桌面上，一不可伸长的柔软轻绳跨过光滑轻质定滑轮，两端分别与A、B相连接，A和滑轮间的轻绳与桌面平行。现将A从静止释放，当B落地时，A还在桌面上。不计空气阻力，重力加速度为g。求：

（1）B落地前的加速度a的大小；

（2）B落地前滑轮对轮轴的压力F大小。

【题目】右图所示的实验装置验证m1、m2组成的系统机械能守恒．m2从高处由静止开始下落，m1上拖着的纸带打出一系列的点，对纸带上的点迹进行测量，即可验证机械能守恒定律．如图给出的是实验中获取的一条纸带：0是打下的第一个点，每相邻两计数点间还有4个点（图中未标出），计数点间的距离如图所示．已知m1＝50 g、m2＝150 g，则（结果均保留两位有效数字）

（1）在纸带上打下计数点5时的速度v＝______m/s；

（2）在打下第“0”到打下第“5”点的过程中系统动能的增量ΔEk＝________ J，系统势能的减少量ΔEp＝______J；（取当地的重力加速度g＝10 m/s2）

（3）若某同学作出v2－h图象如图所示，则当地的重力加速度g＝________m/s2.

【题目】化学兴趣小组为探究SO2的性质，按下图所示装置进行实验。(已知：Na2SO3+H2SO4===Na2SO4+SO2↑+H2O)

请回答下列问题：

(1)装置A中盛放浓硫酸和亚硫酸钠的仪器名称分别是________、________。

(2)反应后，装置B中发生的现象是_________________________________；反应的离子方程式为______________________________；装置C中的现象是___________________________，表现了SO2的________；装置D中现象是_____________________________________________，发生反应的化学方程式为_________________________________________。

(3)装置E的目的是探究SO2与品红作用的可逆性，请写出实验操作及现象_________________________。

(4)F装置的作用是________________________，漏斗的作用是___________________________。

【题目】如图所示是一种延时开关，当S1闭合时，电磁铁F将衔铁D吸下，将C线路接通。当S1断开时，由于电磁感应作用，D将延迟一段时间才被释放。则下列说法中正确的是（ ）

A．由于A线圈的电磁感应作用，才产生延时释放D的作用

B．由于B线圈的电磁感应作用，才产生延时释放D的作用

C．如果断开B线圈的开关S2，无延时作用

D．如果断开B线圈的开关S2，延时将变长

【题目】听下面一段对话，完成五道小题，每小题仅填写一个词。这段对话你将听两遍。

【题目】铅蓄电池的工作原理为Pb＋PbO2＋2H2SO4=2PbSO4＋2H2O。研读下图，下列判断不正确的是( )

A．K闭合时，d电极反应式：PbSO4＋2H2O－2e－=PbO2＋4H＋＋SO42－

B．当电路中转移0.2 mol电子时，Ⅰ中消耗的H2SO4为0.2 mol

C．K闭合时，Ⅱ中SO42－向c电极迁移

D．K闭合一段时间后，Ⅱ可单独作为原电池，d电极为正极

违法和不良信息举报电话：027-86699610 举报邮箱：58377363@163.com

精英家教网