题干

如图,倾角为30°的自动扶梯在电压为380V的电动机带动下以0.4m/s的恒定速率向斜上方运动,电动机的最大输出功率为4.9kW,空载时电动机中的电流为5A,若载人时扶梯的运动速率和空载时相同.设所载人的平均质量为60kg,重力加速度g=10m/s2.不计一切损耗,则扶梯匀速运动过程中(  )

A:站在扶梯上的人不受摩擦力作用

B:扶梯可同时乘载的最多人数为25人

C:扶梯可同时乘载的最多人数为40人

D:无论空载、承载或满载,电动机的输出功率均为4.9kW

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答案(点此获取答案解析)

A,B

同类题3

阅读下文,回答问题。

有事喊董三儿

程宪涛

    董三儿不是我们公司员工,是蹬“倒骑驴”的闲散打工人员。在东北铁岭,称人力三轮车为倒骑驴。董三儿每天比员工来得早,推着倒骑驴站在公司前。见往来的员工笑着打招呼。上班啦!问候里浸淫了无限羡慕。四十余岁高大的汉子,脸上挤满了谄媚的余韵,就格外引人注意了。

    公司是较大的国有企业,员工十三年未涨过工资,普通员工一千三百多块的月薪,与国民经济发展极不适应。公司就像一根鸡肋,仅仅拴住大家的身子,员工身在曹营心在汉。如果多了分外的工作,一次两次三次四次就罢了,时间长了就吹胡子瞪眼,不给领导们好脸色看。大小领导都深感惭愧,也不好意思指手画脚。

    这样就给了董三儿机会。比如,抬桌子、搬椅子、送货物等,员工都懒得多伸一下手。大家顺嘴一句话:找董三儿来。有人到楼下找董三儿,有的甚至推开窗户就喊一声。董三儿乐颠颠地来了,穿着脏的旧衣服,铁塔一样横在办公室门前。大家七嘴八舌指派。董三儿记下说声好嘞。一会儿的工夫就做好。末了余兴未尽的样子,问,还有活儿干没?这热情和态度多雷锋。给董三儿的报酬形式多

样,也许是半车旧报刊,也许是一些劳保用品,比如皮手套、胶皮靴等。这些东西物超所值,远高于董三儿的劳动价值。

    公司有家属区的物业管理,疏通下水、维修上水等,都是班组员工干,后来员工嫌工资挣得少,怠工、停工、罢工。班组长就带头干活儿,后来班组长也撂了挑子,抄着手大眼瞪小眼。物业公司经理没有办法,某次蓦然想起散工董三儿来,他来之能战,战之能胜。董三儿喜欢干水暖维修,卸下的钢管作为废品卖掉,足以抵几天的工钱。董三儿做活儿不偷懒,不嫌脏,一位退休工人家下水道堵塞,董三儿挽起袖子用手掏,脏水脏物挨着鼻子嘴巴,老工人感动得什么似的,用红字写了感谢信送到公司。公司多年没有受过表扬,狠狠地把物业公司表扬一番。物业公司经理恍然大悟,再有苦脏累的活儿,就叫人喊董三儿过来。董三儿来了,似乎什么活儿都能做。物业公司经理说,你自己干不了。董三儿说,俺再找几个人来。操起手机喊了几嗓子,一会儿,几辆倒骑驴匆匆赶来,都是市场上打散工的汉子。

    董三儿笑嘻嘻地对经理说,你老人家看这些活儿,我们哥们儿要养家糊口,蹬倒骑驴也赚个三十五十的,是不是给俺定一个标准?

    物业公司经理手里有小金库,拍了板子说一天六十元,中午管一荤两素盒饭。没有工钱给董三儿时,就用钢管、弯头、水嘴子等充抵,都是从总公司领来的消耗品。这个标准就延续了下来。董三儿熟悉家属区的管路系统,就像掰着自己的手指头。藿三儿听从指挥随叫随到,一个普通员工也能指使,从来没有怨言和二话,满心满意乐呵呵的样子。2011年秋天,供热系统年久失修瘫痪了,公司招标请有关公司维修。董三儿穿着工装来报名。招标人员问:“你来干什么?”董三儿说:“俺来投标。”招标负责人说:“别胡闹,你投标也不能给你。”董三儿问:“为啥。”招标人说:“啥也不为,就是不行。”董三儿讪讪地离开了。后来一家维修公司中标,这家公司做了充分准备,了解整个供热的运行系统。作业现场出现了董三儿,公司负责安全人员好奇。董三儿说,招标时我授权别人去投标。负责安全的人想起来,说:“有一个法人代表叫董浩然。”奄三儿说:“俺就是董浩然。”

同类题4

阅读下列短文,然后从每小题A.B.C.D四个选项中选出能回答所提问题或完成所给句子的最佳答案。

    It seems that school children all over the world complain (抱怨) about their school food. What do students of your age eat for lunch at school in other countries?

Japan

    High schools have dining rooms. They serve everything from noodles to rice, but not burgers and chips. Other children bring food from home, such as cold rice balls, meat or fish, pickles (泡菜) and vegetables. Twice a year parents are invited to have a taste of the food.

United States

A typical menu from a US school is made up of a hamburger with fried potatoes or roast chicken, lettuce and pickles, fruit and cookies. School lunches must also provide at least one third of the daily amount (总量) of necessary nutrition (营养), such as, vitamin A, vitamin C and calcium (钙).

Australia

    Meat pies, sausage rolls (香肠卷) and hotdogs are all traditional dishes in Australian school shops. But as the country pays more attention to children's health, healthier foods have started to appear on school menus. Many schools have used a traffic light system. The sale of red labeled c标注) foods, including cookies, chocolate and soft drinks. Is served only twice a week. Healthier green labeled foods such as sushi, sandwiches, corn and watermelons, however, are available every day.

South Africa

    Most of South African schools do not serve meals at all. Classes end at l; 30 p. m. and students get their own lunches. Many students bring food from home, usually sandwiches.

      Fast food and fried food sell the best among students. As a result, it has caused a rise in obesity c肥胖) among children. But as more people began to realize that being too fat may cause different kinds of serious illnesses, some schools in towns have led the way towards better nutrition. Now students at these schools are offered lunches of porridge with vegetables, such as cabbage, onions, beans, carrots and tomatoes.