问题 选择题

如图所示,半径r=0.8m的光滑圆轨道被竖直固定在水平地面上,圆轨道最低处有一质量为0. 4kg的小球(小球的半径比r小很多)。现给小球一个水平向右的初速度v0,下列关于在小球的运动过程中说法正确的是(g取10m/s2)(    )

A.v0≤4m/s可以使小球不脱离轨道

B.v0≥4m/s可以使小球不脱离轨道

C.设小球能在圆轨道中做完整的圆周运动,在最低点与最高点对轨道的压力之差为24N

D.设小球能在圆轨道中做完整的圆周运动,在最低点与最高点对轨道的压力之差为20N

答案

AC

题目分析: 要使小球不脱离轨道运动,1、越过最高点.2、不越过四分之一圆周;最高点的临界情况mg=解得v==m/s;根据机械能守恒定律得,+mg•2r=,解得v0=;若不通过四分之一圆周,根据机械能守恒定律有: mgr=,解得v0==4m/s。故小球不脱离轨道,v0<4m/s或v0>,故A对,B错;若小球能在圆轨道中做完整的圆周运动,在最高点,由向心力公式:FN1+mg=,在最低点,由向心力公式:FN2-mg=

由根据机械能守恒定律得,mg•2r=,得FN2- FN2=24N,故C正确,D错误

单项选择题 A1/A2型题
阅读理解

You are given many opportunities in life to choose to be a victim or creator. When you choose to be a victim, the world is a cold and difficult place. “They” did things to you which caused all of your pain and suffering. “They” are wrong and bad, and life is terrible as long as “they” are around. Or you may blame yourself for all your problems, thus internalizing(内化)your victimization. The truth is, your life is likely to stay that way as long as you feel a need to blame yourself or others.

Those who choose to be creators look at life quite differently. They know there are individuals who might like to control their lives, but they don’t let this get in the way. They know they have their weaknesses, yet they don’t blame themselves when they fail. Whatever happens, they have choice in the matter. They believe their dance with each sacred(神圣的)moment of life is a gift and that storms are a natural part of life which can bring the rain needed for emotional and spiritual growth.

Victims and creators live in the same physical world and deal with many of the same physical realities, yet their experience of life is worlds apart. Victims relish (沉溺)in anger, guilt, and other emotions that cause others---and even themselves---to feel like victims, too. Creators consciously choose love, inspiration, and other qualities which inspire not only themselves, but all around them. Both victims and creators always have choice to determine the direction of their lives.

In reality, all of us play the victim or the creator at various points in our lives. One person, on losing a job or a special relationship, may feel as if it is the end of the world and sink into terrible suffering for months, years, or even a lifetime. Another with the same experience may choose to first experience the grief, then accept the loss and soon move on to be a powerful creative force in his life.

In every moment and every circumstance, you can choose to have fuller, richer life by setting a clear intention to transform the victim within, and by inviting into your life the powerful creator that you are.

小题1:What does the word “they” in Paragraph 1 probably refer to?

A.People and things around you.

B.Opportunities and problems.

C.Creators and their choices.

D.Victims and their sufferings.小题2:According to Paragraph 2, creators __________.

A.seem willing to experience failures in life

B.possess the ability to predict future life

C.handle ups and downs of life wisely

D.have potential to create something new小题3:What can we learn from Paragraph 3?

A.Creators and victims face quite different things in life.

B.Creators and victims are masters of their lives.

C.Victims can influence more people than creators.

D.Compared with victims, creators are more emotional.小题4:The examples mentioned in Paragraph 4 show that _______________.

A.strong attachment to sufferings in life pulls people into victims.

B.people need family support to deal with challengers in life.

C.it takes creators quite a long time to get rid of their pains.

D.one’s experiences determine his attitude toward life.小题5:What is the author’s purpose in writing this passage?

A.To define victims and creators.

B.To evaluate victims against creators.

C.To explain the relationship between victims and creators.

D.To suggest the transformation from victims to creators.