如图所示,带正电的小球穿在绝缘粗糙直杆上,杆倾角为θ,整个空间存在着竖直向上的匀

题型:选择题

问题:

如图所示,带正电的小球穿在绝缘粗糙直杆上,杆倾角为θ,整个空间存在着竖直向上的匀强电场和垂直于杆斜向上的匀强磁场,小球沿杆向下运动,在a点时动能为100J,到C点动能为零,而b点恰为a、c的中点,在此运动过程中(  )

A.小球经b点时动能为50J

B.小球电势能增加量可能大于其重力势能减少量

C.小球在ab段克服摩擦所做的功与在bc段克服摩擦所做的功相等

D.小球到C点后可能沿杆向上运动

考点:功能关系电势能
题型:选择题

小宇连接好了一个电路,如图所示,但是,小丽认为此电路有缺点,因为没法只让L2亮,而L1不亮。小丽想将此电路改为由S1、S2分别控制L1、L2的并联电路,应该如何改?请你帮她想个解决的办法,要求改动的导线不超过两条。请在图上改动,先在需改动的导线上画“×”,然后用虚线画出改动后的导线,并画出改后的电路图。

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()的闪点<60°C。

A、汽油

B、乙醚

C、煤油

D、机油

E、柴油

题型:选择题

When workers become more efficient, it’s normally a good thing. But lately, it has acted as a powerful brake on job creation. And the question of whether the recent surge in productivity has run its course is the key to whether job growth is finally poised to take off.

One of the great surprises of the economic downturn that began 27 months ago is this.. Businesses are producing only 3 percent fewer goods and services than they were at the end of 2007, yet Americans are working nearly 10 percent fewer hours because of a mix of layoffs and cutbacks in the workweek.

(46) That means high-level gains in productivity--which in the long run is the key to a higher standard of living but in the short run contributes to sky-high unemployment. So long as employers can squeeze dramatically higher output from every worker, they won’t need to hire again despite the growing economy.

(47) On Friday, the Labor Department will release a closely watched March employment report expected to show the pest job growth in three years, driven by stabilization in the economy and a rebound from February snowstorms.

A p March job-growth number-at a time when the economy is growing at only a middling pace--would suggest that the productivity boom has largely run its course. (48) Regardless, the question of what caused the burst in workers’ efficiency is one of the great unanswered questions of the expansion and has huge stakes for the economy over the coming year.

"It is an episode that we’re going to--we, economists in general--are going to want to understand better and look at for a long time," Federal Reserve Chairman Ben S. Bernanke said at a hearing last week in which he described the productivity gains as "extraordinary" and acknowledged he had not foreseen them.

(49) Businesses have certainly not been investing in new equipment that might enable workers to be more efficient-capital expenditures plummeted during the recession and are rebounding slowly. (50) And the structural shifts occurring in the economy are so profound that one would expect productivity to be lower, rather than higher, as people need new training to work in parts of the economy that are growing, such as exports and the clean-energy sector.

So what’s happening As best as anyone can guess, the crisis that began in 2007 and deepened in 2008 caused both businesses and workers to panic.

(47) On Friday, the Labor Department will release a closely watched March employment report expected to show the pest job growth in three years, driven by stabilization in the economy and a rebound from February snowstorms.

题型:选择题

甲乙两国因为领土之争发生严重的武装冲突,甲乙均是《1977年日内瓦四公约第一附加议定书》的成员国,根据该公约的规定,甲国在战争中采取的哪项战争手段和作战方法不属于该公约禁止之列( )

A.甲国攻击或炮击不设防的城镇、乡村或住宅

B.甲国为发起进一步攻击拖延时间因此亮出休战旗要求与乙国谈判

C.甲国命令本国军官和战争人员使用中立国的标志及记号

D.甲国为扰乱乙国的军事计划故意通过无线电频率传递假情报

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凡检查含量均匀度的胶囊剂,可不进行装量差异的检查。()

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