如图所示,一个质量是20kg的小孩从高为2m的滑梯顶端由静止滑下,滑到底端时的速度为2m/s(取
),关于力对小孩做的功,以下结果不正确的是( )
![](https://img.xkw.com/dksih/QBM/2022/2/12/2921909277237248/2922144352911360/STEM/4711d2bd-8b22-4c31-8c92-70c4cdf308d3.png?resizew=213)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/46a6a294d3d7206bcdde5b943dbe94f0.png)
![](https://img.xkw.com/dksih/QBM/2022/2/12/2921909277237248/2922144352911360/STEM/4711d2bd-8b22-4c31-8c92-70c4cdf308d3.png?resizew=213)
A.重力做的功为400J | B.合外力做功为40J |
C.支持力做功为360J | D.阻力做功为360J |
更新时间:2022-02-22 23:00:48
|
【知识点】 多个力做的总功
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【推荐1】如图所示,用轻绳拴一质量
的物体,以加速度
向下减速运动0.4m。g取
,关于物体所受力做的功及能量的变化情况(空气阻力不可忽略),下列说法正确的是( )
![](https://img.xkw.com/dksih/QBM/2022/5/26/2987540802781184/2987957015912448/STEM/deb354d0-6a7a-44fb-8e9a-b8c628da1f78.png?resizew=74)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6967ec3aaf9e7e6a9d90533b8ff61d10.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c6cc233eec4c4c95de6dfd7ee922fc2d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f06d7dc5407015377158ba5251a3d0ec.png)
![](https://img.xkw.com/dksih/QBM/2022/5/26/2987540802781184/2987957015912448/STEM/deb354d0-6a7a-44fb-8e9a-b8c628da1f78.png?resizew=74)
A.重力做功为4J | B.克服拉力做功3J |
C.合外力做功1J | D.机械能减少量5J |
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【推荐2】如图所示,用大小为
,沿水平方向的恒力F作用在质量为
的木箱上,使木箱在水平地面上沿直线运动,已知木箱与地面间的动摩擦因数
,g取
,当木箱从静止开始运动了
时( )
![](https://img.xkw.com/dksih/QBM/2020/8/18/2530712836464640/2531043768279040/STEM/6d41fe50-0227-4625-879f-0e4f2727dcd4.png?resizew=212)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7c3bbd8dabf5d22e4adf5aa7515073b2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d776237845fded133ef34870d44afdb6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/daab4f7805670e4c5a495bb6d6050685.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b1eebd522c4de12f8255e649d3145d51.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e978c77cb0d7eff794447241e9829867.png)
![](https://img.xkw.com/dksih/QBM/2020/8/18/2530712836464640/2531043768279040/STEM/6d41fe50-0227-4625-879f-0e4f2727dcd4.png?resizew=212)
A.力F做的功![]() |
B.重力做的功![]() |
C.克服摩擦力做的功![]() |
D.合力做的功![]() |
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