题目内容
物体从离地面45 m高处做自由落体运动(g取10 m/s2),则下列选项中正确的是( )
A.物体运动3 s后落地 |
B.物体落地时的速度大小为30 m/s |
C.物体在落地前最后1 s内的位移为25 m |
D.物体在整个下落过程中的平均速度为20 m/s |
ABC
:选ABC.由h=
gt2得t=
=3 s
Δh=
gt
-
gt
=25 m,v=gt=30 m/s
=
=
m/s=15 m/s.则A、B、C正确.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132111058338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132111167587.png)
Δh=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132111058338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132111214293.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132111058338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132111276244.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132111292270.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132111323403.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132111385443.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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