题干

如图所示,人沿水平方向用50N的力拉牛,但没有拉动,两者处于势均力敌状态.下列说法中正确的是(    )

A:地面对人的摩擦力与地面对牛的摩擦力是一对相互作用力

B:绳拉牛的力与地面对牛的摩擦力是一对平衡力

C:人拉绳的力小于牛拉绳的力

D:绳拉牛的力小于牛拉绳的力

上一题 下一题 0.0难度 选择题 更新时间:2019-08-01 10:09:26

答案(点此获取答案解析)

B

同类题1

阅读《母亲的金手表》,完成问题。
                                                                              母亲的金手表
                                                                                   琦君
      ①那只圆圆的金手表,以今天的眼光看起来是非常笨拙的,可是那个时候,它是我们全村最漂亮的手表。左邻右舍、亲戚朋友到我家来,听说父亲给母亲带回一只金手表,都要看一下开开眼界。每逢此时,母亲会把一双油腻的手,用稻草灰泡出来的碱水洗得干干净净,才上楼去从枕头下郑重其事地捧出那只长长的丝绒盒子,轻轻地放在桌面上,打开来给大家看。然后,她眯起眼来看半天,笑嘻嘻地说:“也不晓得现在是几点钟了。”我就说:“你不上发条,早都停了。”母亲说:“停了就停了,我哪有时间看手表。看看太阳晒到哪里,听听鸡叫,就晓得时辰了。”我真想说:“妈妈不戴就给我戴吧。”
      ②但我不敢说,我知道母亲绝对舍不得的。我只有趁母亲在厨房里忙碌的时候,才偷偷地去取出来戴一下,在镜子前左照右照一阵又取下来,小心放好。我也并不管它的长短针指在哪一时哪一刻。跟母亲一样,金手表对我来说,不是报时,而是全家紧紧扣在一起的一份保证、一种象征。我虽幼小,却完全懂得母亲珍爱金手表的心意。
      ③后来我长大了,要去上海读书。临行前夕,母亲泪眼婆娑地要把这只金手表给我戴上,说读书赶上课要有一只好的手表。我坚持不肯戴,说:“上海有的是既漂亮又便宜的手表,我可以省吃俭用买一只。这只手表是父亲留给您的最宝贵的纪念品啊。”那时父亲已经去世一年了。
      ④我也是流着眼泪婉谢母亲这份好意的。到上海后不久,我就在同学介绍的熟悉的表店,买了一只价廉物美的不锈钢手表。每回深夜伏在小桌上写信给母亲时,我都会看看手表写下时刻。我写道:“妈妈,现在是深夜一时,您睡得好吗?枕头底下的金手表,您要时常上发条,不然的话,停止摆动太久,它会生锈的哟。”母亲的来信总是叔叔代写的,从不提手表的事。我知道她只是把它默默地藏在心中,不愿意对任何人说。
      ⑤大学四年中,我也知道母亲的身体不太好,可她竟然得了不治之症,这我一点都不知道。她生怕我读书分心,叫叔叔瞒着我。我大学毕业留校工作,第一个月的薪水一领到就买了一只手表,要把它送给母亲。它也是金色的,不过比父亲送的那只江西老表要新式多了。
      ⑥那时正值抗日,海上封锁,水路不通。我于天寒地冻的严冬,千辛万苦从旱路赶了半个多月才回到家中,只为拜见母亲,把礼物献上,却没想到她老人家早已在两个月前就去世了。
      ⑦这份锥心的忏悔,实在是百身莫赎。我是不该在兵荒马乱中离开衰病的母亲远去上海念书的。她挂念我,却不愿我知道她的病情。慈母之爱,昊天罔极1
      ⑧我含泪整理母亲的遗物,发现那只她最珍爱的金手表无恙地躺在丝绒盒中,放在床边的抽屉里。指针停在一个时刻上,但那绝不是母亲逝世的时间。她平时就不记得给手表上发条,何况在沉重的病中。
      ⑨没有了母亲以后的那一段日子,我恍恍惚惚的,任凭宝贵光阴悠悠逝去。有一天,我忽然省悟:徒悲无益,这绝不是母亲隐瞒自己的病情、让我专心完成学业的深意,我必须振作起来,稳步向前走。
     ⑩于是我抹去眼泪,取出金手表,上紧发条,拨准指针,把它放在耳边,仔细听它柔和而有韵律的滴答之音,仿佛慈母在对我频频叮咛,我的心也渐渐平静下来。
【注】①昊天罔极原指天空广大无边,后比喻父母的恩德极大。

同类题4

阅读理解

    After years of research and testing, the hybrid car was developed and put on the market. It' s an interesting and exciting new improvement in today' s world as we look for better ways to protect the quality of the air we breathe and conserve our natural resources.

    The quality of our air is affected by many different things. But one of the largest sources of air pollution is the burning of fossil fuels such as coal and gasoline which is used to power a car' s engine. The EPA has set national standards to help control the level of harmful pollutants sent off into the air, and the automobile industry has acted by producing a hybrid car that uses less gas and therefore causes less pollution.

    A hybrid car is a combination of a regular car that runs on gasoline and an electric car that is battery powered. Some people tend to think that since the hybrid car is partially electric, you have to plug it in to charge it. But that's not how it works. The 144volt battery pack is actually recharged through the energy that is produced when the car's brakes are used. This is referred to as “regenerative braking”, because it generates electricity.

    Although the hybrid car still runs on gasoline most of the time, this helps it use less gas than a regular car. When the driver stops at a traffic light, the engine automatically shuts off to save fuel. Then, as soon as the driver puts the car in gear and touches the gas pedal, the engine starts back up.

    Have you ever ridden in a car with someone who ran out of gas? That probably wouldn't happen if you were riding in a hybrid car. It flashes a warning on its computer screen that says, “I am low on gas”. When it completely runs out, the warning reads, “YOU ARE NOW OUT OF GAS!” Then the electric power supply kicks in to let the driver travel a few more miles to a gas station.