题干

如图所示,金属导轨MNC和PQD,MN与PQ平行且间距为L,所在平面与水平面夹角为α,N、Q连线与MN垂直,M、P间接有阻值为R的电阻;光滑直导轨NC和QD在同一水平面内,与NQ的夹角都为锐角θ。均匀金属棒ab和ef质量均为m,长均为L,ab棒初始位置在水平导轨上与NQ重合;ef棒垂直放在倾斜导轨上,与导轨间的动摩擦因数为μ(μ较小),由导轨上的小立柱1和2阻挡而静止。空间有方向竖直的匀强磁场(图中未画出)。两金属棒与导轨保持良好接触。不计所有导轨和ab棒的电阻,ef棒的阻值为R,最大静摩擦力与滑动摩擦力大小相等,忽略感应电流产生的磁场,重力加速度为g。

(1)若磁感应强度大小为B,给ab棒一个垂直于NQ、水平向右的速度v1,在水平导轨上沿运动方向滑行一段距离后停止,ef棒始终静止,求此过程ef棒上产生的热量;

(2)在(1)问过程中,ab棒滑行距离为d,求通过ab棒某横截面的电荷量;

(3)若ab棒以垂直于NQ的速度v2在水平导轨上向右匀速运动,并在NQ位置时取走小立柱1和2,且运动过程中ef棒始终静止。求此状态下最强磁场的磁感应强度及此磁场下ab棒运动的最大距离。


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同类题2

通读下面短文, 掌握其大意, 然后在每小题所给的四个选项中, 选出一个最佳答案, 并将答题卡上对应的选项涂黑。

    My parents are busy with their work every day. You can't see there is love 1 them. They don't act in the romantic(浪漫的)2that I read in books or I see on TV.

    One day, while Mom was sewing(缝) a quilt,I 3 beside her. “Mom, I have a question,” I said after a while.

    “What?” she asked.

    “Is there love between you and Dad?” I asked her in a very low voice.

    She stopped sewing and 4 her head. Then she bowed her head and went on sewing.

    I thought I had hurt her. At last I heard my mother say, “Susan, look at this thread(线). Sometimes it appears, but most of it disappears in the quilt. It makes the quilt5. If life is a quilt, then love should be a thread. It can hardly be seen, but it's 6 there.”

    I couldn't understand her 7 the next spring. My father suddenly got sick. Mom had to stay with him in the hospital for a month.

    After they 8, my mother helped my father walk slowly down the country road every day. My father had never been so gentle.

    “Dad, how are you 9 now?” I asked him one day. “Susan, don't worry about me,” he said. “I just like walking with your Mom.”

     Once I thought 10 meant flowers, gifts and sweet kisses. But from this experience, I understand that it is just a thread in the quilt of our life . It is inside, making life strong and warm.

同类题4

任务型阅读

    At what age does a child became an adult?____Here are a few examples.

    First, in some North American Indian culture, a boy became a man around the age of 13. At that time, he would go into the woods alone, without food or water, for several days.____Girls became adult women as soon as they were old to have babies, also around the age of 12 or 13.

    In the Jewish religion, children spend years studying their history and religion. Then, at age of 13 for boys and 12 for girls, they go through an important religious ceremony.____

    In Japan today, young people become legal adult at age 20. Each year on January 15th, they celebrate “Coming-of-Age Day”, when the 20-year-olds in a town are invited to attend to special ceremony.____

    Finally, in the United States, the passage into adulthood takes several years. American teenagers look forward to their 16th birthday because in most states that is the age when can get a driver's license. The legal age of adulthood is 18, when Americans can vote, get married and work full-time. However, they must wait until age 21 to buy alcohol.____

A. Many people celebrate their 21st birthday by having a drink with friends in a bar.

B. It's hard to answer the question.

C. The answer depends on your culture or religion.

D. From that day, they are adults, and they become responsible for their own religious development.

E. When he returned safely, he became an adult man.

F. The teenagers are not allowed to drink alcohol.

G. They wear traditional clothes, listen to speeches and visit old friends.