题干

如图所示,图中两组曲线中实线代表电场线(方向未画出)、虚线代表等势线,点划线是 一个带电粒子仅在电场力作用下从A到B的运动轨迹,下列说法正确的是           (   )

A:粒子一定带正电

B:粒子的动能一定是越来越大

C:粒子的电势能一定是越来越大

D:A点的电势一定高于B点的电势

上一题 下一题 0.0难度 选择题 更新时间:2016-01-21 04:14:25

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B

同类题1

任务型阅读

    US City Bans Texting while Walking

    Parents usually teach their children how to cross the street safely, by looking both ways for cars. But do they also teach them to put away their cell phones?

    The city of Honolulu, Hawaii wants everyone to learn that lesson____Beginning on October 24, you could be fined from $15 to $99 if you step into a Honolulu street while looking at your phone. Honolulu is the first major U. S. city to ban what is called "distracted (分散注意) walking. " It recently passed a law in a seven to two vote. The law says; “No pedestrian shall cross a street or highway while viewing a mobile electronic device. "____

    The law's creators hope it will lower the number of people hit and killed by cars in the city. Mayor Kirk Caldwell told Reuters news agency, "We hold the unfortunate distinction (区别) of being a major city with more pedestrians being hit in crosswalks, particularly our elders, than almost any other city in the country. "

    The law includes all electronic devices with screens: cell phones, tables, gaming devices, digital cameras and laptop computers____Pedestrians may use such devices in the street to call emergency services and rescue workers, such as firefighters and police officers.

    ____The Governors Highway Safety Association, or GHSA, says pedestrian deaths in the United States increase 25 percent between 2010 and 2015. That trend continued in 2016 with the number of pedestrian deaths rising to almost 6000, 11% higher than in 2015.

    If you still want to text while walking, you could avoid being fined in Honolulu (and be safer, in general) by using a voice-controlled digital(数字的) assistant such as Siri or Google Assistant____

A. The law does permit an exception.

B. Or you could just wait until you are again, safely, off the street.

C. You will be sentenced to prison while using cell phones in the street.

D. Pedestrian deaths have been increasing as the use of cell phones rises.

E. Texting while crossing the street will soon be banned in the city.

F. The law permits people to watch TV while crossing the street.

G. In other words, do not look at a screen when you cross the street or you could be fined.

同类题4

阅读下面两篇短文,完成小题。

河中石兽

    沧州南一寺临河干,山门圮于河,二石兽并沉焉。阅十余岁,僧募金重修,求二石兽于水中,竟不可得,以为顺流下矣。棹数小舟,曳铁钯,寻十余里无迹。

    一讲学家设帐寺中,闻之笑曰:“尔辈不能究物理。是非木杮,岂能为暴涨携之去?乃石性坚重,沙性松浮,湮于沙上,渐沉渐深耳。沿河求之,不亦颠乎?”众服为确论。

    一老河兵闻之,又笑曰:“凡河中失石,当求之于上流。盖石性坚重,沙性松浮,水不能冲石,其反激之力,必于石下迎水处啮沙为坎穴。渐激渐深,至石之半,石必倒掷坎穴中。如是再啮,石又再转。转转不已,遂反溯流逆上矣。求之下流,固颠;求之地中,不更颠乎?”

    如其言,果得于数里外。然则天下之事,但知其一,不知其二者多矣,可据理臆断欤?

刘翀读书

    刘翀偶得古兵书,伏读经年,自谓可将①十万。会②有土寇,自练乡兵与之角,全队溃覆,几为所擒。又得古水利书,伏读经年,自谓可使千里成沃壤。绘图列说于州官。州官亦好事,使试于一村。沟洫③甫④成,水大至,顺渠灌入,人几为鱼。由是抑郁不自得,恒独步庭阶,曰:“古人岂欺我哉?”

【注释】①将:率领,带领。②会:恰逢,正赶上。③沟洫:田间水渠。④甫:刚,才。