题干

如图所示,小明每次都让小车在斜面上同一高度由静止释放,然后在粗糙程度不同的水平面上运动,探究“运动和力的关系”.关于这一实验,下面叙述中错误的是(   )

A:在同一高度静止释放小车是为了保证小车在水平面上开始运动时惯性相同

B:小车的轮子起到减小摩擦的作用

C:小车下滑过程中重力势能转化为动能

D:小车滑下斜面后,由于惯性在水平面上还能滑行一段距离

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A

同类题4

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    My husband hasn't stopped laughing about a funny thing that happened to me. It's funny now but it wasn't at the time.

    Last Friday, after doing all the family shopping in town, I wanted a rest before catching the train, so I bought a newspaper and some chocolate and went into the station coffee shop — that was a cheap self-service place with long tables to sit at. I put my heavy bag down on the floor, put the newspaper and chocolate on the table to keep a place, and went to get a cup of coffee.

    When I went back with the coffee, there was someone in the next seat. It was one of those wild-looking youngsters, with dark glasses and worn clothes, and hair colored bright red at the front. Not so unusual these days. What did surprise me was that he'd started to eat my chocolate!

    Naturally, I was annoyed. However, to avoid trouble — and really I was rather uneasy about him — I just looked down at the front page of the newspaper, tasted my coffee and took a bit of chocolate. The boy looked at me closely. Then he took a second piece of my chocolate. I could hardly believe it. Still I didn't dare to start an argument. When he took a third piece, I felt more angry than uneasy. I thought, "Well, I shall have the last piece." And I got it.

    The boy gave me a strange look, and then stood up. As he left he shouted out. "This woman's crazy!" Everyone stared. That was embarrassing enough, but it was worse when I finished my coffee and got ready to leave. My face went red — as red as his hair — when I realized I'd made a mistake. It wasn't my chocolate that he'd been taking. There was mine, unopened, just under my newspaper.