题干

如图所示,有一倾角为θ的斜面体B静置在水平地面上,物体A放在斜面上且与B保持相对静止。现对斜面体B施加向左的水平推力,使物体A和斜面体B一起向左做加速运动,加速度从零开始逐渐增大,直到A和B开始发生相对运动,则关于A物体受到B物体的支持力FN和摩擦力Ff,下列说法正确的是                           (   )

A:FN增大,Ff增大

B:FN不变,Ff不变

C:FN增大,Ff先减小后增大

D:FN减小,Ff先增大后减小

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答案(点此获取答案解析)

C

同类题1

阅读下面短文,掌握其大意,然后从各题所给的A、B、C、D四个选项中,选出可以填入空白处的最佳选项,并在答题卡上将该项涂黑。

    As I drove my blue Buick into the garage, I saw that a yellow Oldsmobile was 1too close to my space. I had to drive back and forth to get my car into the 2 space. That left 3 enough room to open the door. Then one day I arrived home 4 , and just as I turned off the engine, the yellow Oldsmobile entered its space — too close to my car, 5 . At last I had a chance to meet the driver. My patience had 6 and I shouted at her, “Can't you see you're not 7 me enough space? Park farther over.” Banging(猛推) open her door into 8 , the driver shouted back: “Make me!” 9 this she stepped out of the garage. Still, each time she got home first, she parked too close to my 10 . Then one day, I thought, “What can I do?” I soon found 11 . The next day the woman 12 a note on her windshield(挡风玻璃):

    Dear Yellow Oldsmobile,

    I'm sorry my mistress(女主人) shouted at yours the other day. She's been sorry about it. I know it because she doesn't sing anymore while 13 . It wasn't like her to scream 14 . Fact is, she'd just got bad news and was taking it out on you two. I 15 you and your mistress will 16 her.

Your neighbor,

Blue Buick

    When I went to the 17 the next morning, the Oldsmobile was gone, but there was a note on my windshield:

Dear Blue Buick,

    My mistress is sorry, too. She parked so 18 because she just learned to drive. We will park much farther over after this. I'm glad we can be 19 now.

Your neighbor,

Yellow Oldsmobile

    After that, whenever Blue Buick 20 Yellow Oldsmobile on the road, their drivers waved cheerfully and smiled.