问题 不定项选择

如图所示,质量为M、长度为L的小车静止在光滑的水平面上。质量为m的小物块(可视为质点)放在小车的最左端。现用一水平恒力F作用在小物块上,使物块从静止开始做匀加速直线运动,物块和小车之间的摩擦力为Ff。物块滑到小车的最右端时,小车运动的距离为l。在这个过程中,以下结论正确的是

[ ]

A.物块到达小车最右端时具有的动能为(F-Ff)(L+l)

B.物块到达小车最右端时,小车具有的动能为Ffl

C.物块克服摩擦力所做的功为Ff(L+l)

D.物块和小车增加的机械能为Fl

答案

ABC

选择题
填空题

Marks & Spencer has a very good reputation for job security and looking after its staff, with things like good perks, (1) , that sort of thing. Do those things actually (2)
I think it is, it is very important. When people have been working (3) , and they may have been in from seven or eight o’clock in the morning, they can come off the sales floor and can go to (4) and obviously they can have tea, coffee, or (5) , and can then buy at very reduced rates (6) , if they want one, or a roll and cheese, in a pleasant environment, (7) , food of the highest quality, there’re areas where they can (8) , or play pool or something, yeah, that is very important because they need (9) . At busy times, they need to get away from it, they need to be able to relax. In terms of all the (10) we’ve got, that is very important, when people know that they will be having medicals, and (11) is another thing, obviously there’s (12) that they will buy which they will be able to buy (13) . For Christmas bonus, we give all our general staff (14) which is guaranteed, and the (15) of that, actually, at the busiest time of the year when they’re (16) and working hard, is fantastic and to see their faces as you (17) with 10% of their salary in it. I believe the environment that you work in, (18) that you work with, the way you are treated, (19) , and the fact that your views are listened to, and you feel you are consulted, that makes people (20) and makes them get up and come to work in the morning.