题干

“快乐向前冲”节目中有这样一种项目,选手需要借助悬挂在高处的绳飞跃到鸿沟对面的平台上,如果已知选手的质量为m,选手抓住绳由静止开始摆动,此时绳与竖直方向夹角为α,如图所示,不考虑空气阻力和绳的质量(选手可看为质点),下列说法正确的是

A:选手摆动到最低点时所受绳子的拉力等于mg

B:选手摆到最低点时所受绳子的拉力大于mg

C:选手摆到最低点时受绳子的拉力大于选手对绳子的拉力

D:选手摆到最低点的运动过程为匀变速曲线运动

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答案(点此获取答案解析)

B

同类题5

阅读下面短文,从短文后各题所给的四个选项(A, B, C和D)中,选出可以填入空白的选项。

    My wife and I were walking through the parking lot at the supermarket the other day. We noticed a huge truck 1 about a foot into the next parking space. There was plenty of room in its own space, 2 the driver had chosen to park very poorly and made sure that 3 could use the space next to his.

    My first 4 was “Why do people act like such idiots (白痴)?”

    “What a 5 that people have to do things like that.” My wife said.

    I stopped and looked around at the rest of the parking lot. There were a good five hundred 6 and 99% of them were parked well. Their drivers had shown the 7 necessary to park in a way that still 8 other people to park.

    “Think about it,” I said. “Only one 9 parks poorly and we start using ‘people' to describe the driver.” The 10 of the matter is that we forget about the thousands of people who behave themselves when we see one person doing something 11.

    I've been 12 for many years, and the percentage of good drivers is always 13 than the percentage of poor drivers. “People” don't necessarily drive poorly, but individuals do.

    My wife and I almost didn't 14 the many cars that were parked well because the car that was parked poorly caught our 15. It is true that we're far less 16 to see the positive side of things if we keep 17 on the negative. Once we fall into this trap, how many of the wonderful things in the world will we 18?

    Our lives are ours to live, and the 19 we see our world is up to us. Remember: the rude person truly is a(n) 20, and not really worth the time or effort we spend thinking about him or her.