如图17所示,光滑绝缘水平桌面上固定一绝缘挡板P,质量分别为mA和mB的小物块A

题型:计算题

问题:

如图17所示,光滑绝缘水平桌面上固定一绝缘挡板P,质量分别为mA和mB的小物块A和B(可视为质点)分别带有+QA和+QB的电荷量,两物块由绝缘的轻弹簧相连,一不可伸长的轻绳跨过定滑轮,一端与物块B连接,另一端连接轻质小钩。整个装置处于正交的场强大小为E、方向水平向左的匀强电场和磁感应强度大小为B、方向水平向里的匀强磁场中。物块A,B开始时均静止,已知弹簧的劲度系数为K,不计一切摩擦及AB间的库仑力,在运动过程中物块A、B所带的电荷量不变,物块B不会碰到滑轮,物块A、B均不离开水平桌面。若在小钩上挂一质量为M的物块C并由静止释放,可恰使物块A对挡板P的压力为零,但不会离开P,则

(1)求物块C下落的最大距离;

(2)求小物块C下落到最低点的过程中,小物块B的电势能的变化量、弹簧的弹性势能变化量;

(3)若C的质量改为2M,求小物块A刚离开挡板P时小物块B的速度大小以及此时小物块B对水平桌面的压力。

考点:带电粒子在电场中的加速
题型:计算题

现有一个由两证券W和Q组成的组合,这两种证券完全正相关,它们的投资比重分别为0.90、0.10。如果W的期望收益率和标准差都比Q大,那么()。

A.该组合的期望收益率一定等于Q的期望收益率

B.该组合的标准差不可能大于Q的标准差

C.该组合的期望收益率一定小于Q的期望收益率

D.该组合的标准差一定大于Q的标准差

题型:计算题

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项,选项中有两项为多余选项。

Are you truly happy? ___1___ These are important questions for anyone who is seeking happiness to ask themselves.The following are a few tips that I follow to create happiness in my life.

● Make a plan for attaining goals that you believe will make you happy.Your moods will very likely increase if you are going after something you value.

●Surround yourself with happy people.___2___On the contrary, if you are around people who are happy, their emotional state will be infectious.

●When something goes wrong, try to figure out a solution instead of being absorbed in self -pity.Truly happy people don’t allow setbacks to affect their mood because they know that with a little thought they can turn the circumstances back to their favor.

____3____These few minutes will give you the opportunity to focus on the positive things in your life and will lead you to continuous happiness.

____4____You can treat yourself to lunch, take a long, relaxing bath or simply spend a few extra minutes on your appearance.Then you will be subconsciously(下意识地)putting yourself in a better mood.

●Finding the humor in situations can also lead to happiness.Find a way to make light of a situation that would otherwise make you happy.

●Keeping healthy is another way to achieve happiness._____5_____.

A.It is easy to begin to think negatively when you are surrounded by people who think that way.

B.Being overweight or not eating nutritious foods can have a negative effect on your mood.

C.Do you ever know what it means to be happy and what it takes to achieve happiness?

D.It’s also important to take some time each day to do something nice for yourself.E.True happiness is hard to reach for most of us.

F.Spend a few minutes each day thinking about the things that make you happy.

G.Speak your trouble out to your close friends openly.

题型:计算题

DIC早期病人首选的抗凝血药物是()

A.肝素

B.双嘧达莫

C.阿司匹林

D.氨甲苯酸

E.鱼精蛋白

题型:计算题

Excel应用程序窗口最下面一行称作状态栏,当输入数据时,状态栏显示()。

A.就绪

B.输入

C.编辑

D.等待

题型:计算题

在起飞和复飞时,FCU上的速度窗显示:().

A.机组人工输入的FCU速度且灯灭

B.机组人工输入的MCDU速度且灯灭

C.白色虚线和点亮:管理速度,如V2或存储的VAPP(进近速度)被FMGS自动使用

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