题干

如图所示,在a点由静止释放一个质量为m,电荷量为q的带电粒子,粒子到达b点时速度恰好为零,设ab所在的电场线竖直向下,a、b间的高度差为h,则(   )

A:带电粒子带负电

B:a、b两点间的电势差Uab= mghq

C:b点场强大于a点场强

D:a点场强大于b点场强

上一题 下一题 0.0难度 选择题 更新时间:2017-04-21 12:40:37

答案(点此获取答案解析)

A,B,C

同类题2

阅读下面文字,回答小题。

梨花的春天

宗满德

    ①春天是从一叶梨花瓣走进人间的。

    ②静谧祥和的夜晚,星星丢给大地一些眼色,黄河里追逐的浪花露出银白的乳牙,一口一口地咬着石砌的堤岸。一粒石子落下来,惊醒一河春梦。露珠在岸边的小草上打盹,月亮盛了半碗。蒸腾上升的水汽,在百年梨树群中氤氲。走过冬天的游子,在梨园守夜,轻轻地哼一曲《北国之春》,缓缓的黄河水泛起涟漪。

    ③阳光错落地从梨树群中穿梭,晨露紧紧地咬了一夜,刚松了一口气,就从树枝上滑落。小草伸出碧绿的小手,低声地吟唱。等待了整整一个冬天,站着的,立着的,都是那样的新颖,那样的鲜活。春天的早晨从最后一个冬夜里开始,预备着上演五彩缤纷的舞会。

    ④主角登场了。叶子还没有发芽,花就开了。热烈,闪亮,胜过炽热的太阳。白衣天仙下凡吧,纯粹,脱俗,灵秀,远隔尘世。皇后出宫吧,抿着嘴,敛着胸,曼妙,轻盈,似在天上,又在民间;朝饮白露,夕餐落英。山姑待字吧,粉着脸,描着一丝淡眉,穿着一件短裙,绛红中透着新绿。一个冬天没有下地干活,白皙的面,光亮滋润。轻轻地吻一下吧,树下巴望的情郎。官窑的白瓷器吧,五枚清亮清亮的盘儿盛着金色的花蕊,还有一粒昨夜刚刚凝炼的银珠。伸开手掌,怕它掉在地上;张开口,怕它飞走。伫立着,凝视着,听花瓣与花蕊轻轻地合唱春的恋歌。

    ⑤树枝则一律裸着,不着一字。一个冬天的努力,都献给了花儿。不害羞的花儿顺着根顺着茎,从土里升起来,挂在枝上,尽情地表演艺术体操。一阵微风吹来,一些娇气的花儿夭折了,从枝头上飘下来,归入土中。叶子是后盾,铁一样坚硬,都埋进枝桠里面,不露声色,不出风头,不争春光。全身的力气和营养,都向一个方向输送。平静地等待是一种内力,没有怨悔地给予是一种品格,低调地劳作是一种风度。花儿开了,还怕没有绿叶,还怕没有果实吗?保持沉着,让花苞绽放吧。资*源%库

    ⑥谁能告诉我,为什么这样地纯,这样地白?梨花给予人间的不仅是春的温柔,也许还有冬的风骨。

    ⑦坐在梨树下,感觉很清爽。空气过滤了一遍,带着蜜意,加了气压,醇厚,浓酽,向着鼻孔往肺里冲,揭开毛孔往里钻。凉凉的,清清的,每呼吸一次就增加一点力量。伸开臂膀吧,全身的肌肉都浸透了氧气,鲜活鲜活的。那美丽的姑娘,如金的光芒,点缀满树的梨花,笑一笑,挥洒出无数的珍珠玉盘,雪一样洁白,玉一样透彻。

    ⑧雪是白的。梨花是白的。骨头也是白的。

    ⑨梨叶长出来了,梨花就纷纷落地。梨成熟了,梨叶就要落地。

    ⑩长肉的骨头看不着。春天里飞雪,是梨花,不是白雪。白雪呢,藏在冬天里,梨花看不着,就如骨头长在血肉里。

    ⑪忙碌的日子,结识许多陌生的面孔。熟识的心跳都在花朵上律动。脚步匆匆,又来又去,草地上没有留下一个脚印。不用凝神,不用注目,随意地看一看,每一朵梨花都认识我,都盛满笑意,都那么温暖,那么善良,那么善解人意。我生命中的每一天都令我欣喜。往日的哀怨和伤痛,曾经的忧愁和苦难,都消逝在这洁白纯净的光波里。

    ⑫梨花开了,春天慢慢地去了。人间落英无数。

(选自《新群文读本》,西南师范大学出版社,2015年)

同类题4

 完形填空
    Time is very important in our life. However, I had never realized it until I received a beautiful gold watch from my father one day when I was 19 years old. This watch always 1 me the importance of time in my life.
   It was a cold rainy day. My father asked me to go to the 2to pick up my uncle and take him home. I should have arrived there before 4:30p.m. We had a basketball match at school that afternoon and the match was so 3that I forgot the time. When the match was nearly over, I suddenly remembered my uncle and hurried to the airport .It was too late. He had left the airport and take a taxi to our house.
   I was very worried that my father would complain 4the thing. As soon as I entered the living room, I saw my uncle in the sofa looking very tired. I do not 5uncle and my father .I said hello to them in a very low voice .My father didn’t say 6.Instead, he asked me to sit7 him. “Peter, did you have a good time today?” I felt so sorry and answered in a 8 voice. “Yes, Dad, but I ’m really sorry .This will9happen again. I promise.”My father handed me a box with a beautiful gold watch inside .It was a gift my uncle bought for him. He gave it to me and said, “I hope you have learned something important today, and this watch will help you remember the importance of time.”
   The watch has been with me for twelve years .I wear it not because of its price, but because of 10I learned. It tells me to respect(重视)and never be late to do what I have promised to .