题目内容
(10分).质量为500吨的机车以恒定的功率由静止出发,经5min行驶2.25km,速度达到最大值54km/h,设阻力恒定。问:
(1)机车的功率P多大?
(2)机车的速度为36 km/h时机车的加速度a多大?
(1)机车的功率P多大?
(2)机车的速度为36 km/h时机车的加速度a多大?
(1)
(2) ![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144818939744.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241448188771500.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144818939744.png)
试题分析:以机车为研究对象,机车从静止出发至达速度最大值过程,根据动能定理得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144819017927.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144819064658.png)
由以上两式得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241448188771500.png)
(2)(4分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241448192981081.png)
当机车速度v="36" km/h时机车的牵引力
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144819469981.png)
根据牛顿第二定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144819657623.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824144818939744.png)
点评:本题需要注意功的另一个求法W=Pt,前提条件是功率不变
![](http://thumb2018.1010pic.com/images/loading.gif)
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