如图所示,半圆形光滑凹槽放在光滑的水平面上,小滑块从凹槽边缘点A由静止释放,经最

题型:多选题

问题:

如图所示,半圆形光滑凹槽放在光滑的水平面上,小滑块从凹槽边缘点A由静止释放,经最低点B,又向上到达另一侧边缘点C.把从点A到达点B称为过程Ⅰ,从点B到达点C称为过程Ⅱ,则(  )

A.过程Ⅰ中小滑块减少的势能等于凹槽增加的动能

B.过程Ⅰ小滑块动量的改变量等于重力的冲量

C.过程Ⅰ和过程Ⅱ中小滑块所受外力的冲量相等

D.过程Ⅱ中小滑块的机械能的增量等于凹槽动能的减少量

考点:机械能守恒定律
题型:多选题

裸子植物和被子植物的主要特征是[ ]

A.种子外均有果皮包被

B.都有真正的花

C.由子房发育为果实

D.由胚珠发育成种子

题型:多选题

如图甲所示,螺线管的匝数n=1000,横截面积S=20 cm2,总电阻r=0.6 Ω,与螺线管并联的外电阻R1=4 Ω、R2=6 Ω。若穿过螺线管的磁场的磁感应强度按图乙所示的规律变化,试求R1上消耗的电功率。

题型:多选题

局域网常用的拓扑结构一般不包括()。

A.总线形

B.环形

C.网状形

D.星形

题型:多选题

Believe it or not, optical illusion can cut highway crashes.

Japan is a case in point. It has reduced automobile crashes on some roads by nearly 75 percent using a simple optical illusion. But stripes, called chevrons, painted on the roads make drivers think that they are driving faster than they really are, and thus drivers slow down.

Now the American Automobile Association Foundation for Traffic Safety in Washington D.C. is planning to repeat Japan’s success. Starting next year, the foundation will paint chevrons and other patterns of stripes on selected roads around the country to test how well the patterns reduce highway crashes.

Excessive(too great) speed plays a major role in as much as one fifth of all fatal traffic accidents, according to the foundation. To help reduce those accidents, the foundation will conduct its tests in areas where speed-related hazards (danger) are the greatest curves, exit slopes, traffic circles, and bridges.

Some studies suggest that straight, horizontal bars painted across roads can initially cut the average speed of drivers in half. However, traffic often returns to full speed within months as drivers become used to seeing the painted bars.

Chevrons, scientists say, not only give drivers the impression that they are driving faster than they really are but also make a lane appear to be narrower. The result is a longer lasting reduction in highway speed and the number of traffic accidents.

The American Automobile Association Foundation for Traffic Safety plans to()

A. try out the Japanese method in certain areas

B. change the road signs across the country

C. replace straight, horizontal bars with chevrons

D. repeat the Japanese road patterns

题型:多选题

用于鉴别生物碱的试剂是()

A.碘化铋钾

B.碱性苦味酸

C.α-萘酚-浓硫酸

D.硫酸铜

E.浓硝酸

更多题库