题干

如图所示,一个劈形物体M放在固定的斜面上,上表面水平,在水平面上放有光滑小球m,劈形物体从静止开始释放,则小球在碰到斜面前的运动轨迹是:

A:沿斜面向下的直线

B:抛物线

C:竖直向下的直线

D:无规则的曲线

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C

同类题4

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    When you meet someone for the first time, you will get a quick idea in your mind of that person in the first moment. Your feelings about other people, however, are really just show the way that you look at yourself.

    So you can allow others to be the mirror to see your own feelings of self-worth more clearly. And, you can see the people you don't like as mirrors to show you what you are not accepting about yourself.

    To live peacefully with others, you will need to learn patience. A big challenge is to let your judgment of others be a lifelong research of yourself. Your task is to consider all the judgments you make onto others carefully and to begin to see whether you can use them to help yourself to become better.

    Several days ago I had a business lunch with a man who showed objectionable table manners. My first feeling was that he was impolite. When I noticed that I was judging him, I stopped and asked myself what I was feeling. I discovered that I was nervous to be seen with someone who was eating with his mouth open.I was very surprised to find how much I cared about how the other people in the restaurant judged me.

    Remember that your judgment of someone will not stop you from becoming like him. Just because I think my lunch partner impolite, it does not prevent me from looking or acting like him. In the same way, my patience to him would not make me eat food with my mouth open.

    When you get close to life in this way, those whom you hate and those whom you love can be seen as mirrors, guiding you to discover parts of yourself that you dislike and to accept your greatest personalities you are proud of.

同类题5

果蝇的灰体(E)对黑檀体(e)为显性;短刚毛和长刚毛是一对相对性状,由一对等位基因(B,b)控制.这两对基因位于常染色体上且独立遗传.用甲、乙、丙三只果蝇进行杂交实验,杂交组合、F1表现型及比例如图:

(1)根据实验一和实验二的杂交结果,推断乙果蝇的基因型可能为____ 或____ .若实验一的杂交结果能验证两对基因E,e和B,b的遗传遵循自由组合定律,则丙果蝇的基因型应为____ .

(2)实验二的F1中与亲本果蝇基因型不同的个体所占的比例为____ .

(3)在没有迁入迁出、突变和选择等条件下,一个由纯合果蝇组成的大种群个体间自由交配得到F1,F1中灰体果蝇8400只,黑檀体果蝇1600只.F1中e的基因频率为____ ,Ee的基因型频率为____ .亲代群体中灰体果蝇的百分比为____ .

(4)灰体纯合果蝇与黑檀体果蝇杂交,在后代群体中出现了一只黑檀体果蝇.出现该黑檀体果蝇的原因可能是亲本果蝇在产生配子过程中发生了基因突变或染色体片段缺失.现有基因型为EE、Ee和ee的果蝇可供选择,请完成下列实验步骤及结果预测,以探究其原因.(注:一对同源染色体都缺失相同片段时胚胎致死;各型配子活力相同)实验步骤:

①用该黑檀体果蝇与基因型为____ 的果蝇杂交,获得F1

②F1自由交配,观察、统计F2表现型及比例.

结果预测:

Ⅰ.如果F2表现型及比例为____ ,则为基因突变;

Ⅱ.如果F2表现型及比例为____ ,则为染色体片段缺失.