题目内容
有两组同样的砖,甲组一块,乙组二块,每块砖的长:宽:高=4:2:1.要使这两组砖对地面的压强相等.下面哪种放法是对的?(砖平放是指长和宽着地,侧放是指长和高着地,竖放是指宽和高着地.)( )A.甲组砖竖放,乙组两块砖沿竖直方向叠加平放
B.甲组砖竖放,乙组两块砖沿竖直方向叠加侧放
C.甲组砖竖放,乙组两块砖沿竖直方向叠加竖放
D.甲组砖平放,乙组两块砖沿竖直方向叠加平放
【答案】分析:比较物体对地面压强的大小,可以根据公式p=
计算出压强大小再进行比较;对于同一块砖来说,无论怎样放置,对地面的压力不变,都等于砖的重力,但地面的受力面积发生了变化.
解答:解:由于砖的长:宽:高=4:2:1,设砖的长、宽、高分别为4a、2a、a.
A、甲组对地面压强为:p甲=
=
=
;乙组对地面的压强为:p乙=
=
=
;所以甲、乙两组放法不对.A错误.
B、甲组对地面压强为:p甲=
=
=
;乙组对地面的压强为:p乙=
=
=
;所以甲、乙两组放法合理,B正确.
C、甲组对地面压强为:p甲=
=
=
;乙组对地面的压强为:p乙=
=
=
;所以甲、乙两组放法不对,C错误.
D、甲组对地面压强为:p甲=
=
=
;乙组对地面的压强为:p乙=
=
=
;所以甲、乙两组放法不对.D错误.
故选B.
点评:公式p=
是计算压强普遍适用的公式,该题计算难度不大,但要注意砖的不同放置方法,其受力面积不同,尤其是两块砖叠放时更要注意.
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/0.png)
解答:解:由于砖的长:宽:高=4:2:1,设砖的长、宽、高分别为4a、2a、a.
A、甲组对地面压强为:p甲=
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/1.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/2.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/3.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/4.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/5.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/6.png)
B、甲组对地面压强为:p甲=
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/7.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/8.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/9.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/10.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/11.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/12.png)
C、甲组对地面压强为:p甲=
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/13.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/14.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/15.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/16.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/17.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/18.png)
D、甲组对地面压强为:p甲=
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/19.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/20.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/21.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/22.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/23.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/24.png)
故选B.
点评:公式p=
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104175047022200400/SYS201311041750470222004006_DA/25.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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有两组同样的砖,甲组一块,乙组二块,每块砖的长:宽:高=4:2:1.要使这两组砖对地面的压强相等.下面哪种放法是对的?(砖平放是指长和宽着地,侧放是指长和高着地,竖放是指宽和高着地.)( )
A、甲组砖竖放,乙组两块砖沿竖直方向叠加平放 | B、甲组砖竖放,乙组两块砖沿竖直方向叠加侧放 | C、甲组砖竖放,乙组两块砖沿竖直方向叠加竖放 | D、甲组砖平放,乙组两块砖沿竖直方向叠加平放 |
有两组同样的砖,甲组一块,乙组二块,每块砖的长:宽:高=4:2:1.要使这两组砖对地面的压强相等.下面哪种放法是对的?(砖平放是指长和宽着地, 侧放是指长和高着地,竖放是指宽和高着地.)
A.甲组砖竖放,乙组两块砖沿竖直方向叠加平放 |
B.甲组砖竖放,乙组两块砖沿竖直方向叠加侧放 |
C.甲组砖竖放,乙组两块砖沿竖直方向叠加竖放 |
D.甲组砖平放,乙组两块砖沿竖直方向叠加平放 |