题目内容
汽车发动机的功率为150 kW,若其总质量为5 t,在水平路面上行驶时,所受阻力恒定为5.0×103N,求:(1)汽车保持额定功率从静止启动后能达到的最大速度是 m/s;
(2)若汽车保持0.5m/s2的加速度做匀加速启动,这一过程能持续时间为 s。
(2)若汽车保持0.5m/s2的加速度做匀加速启动,这一过程能持续时间为 s。
30m/s 40s
试题分析:(1)当牵引力等于阻力时,速度达到最大,即
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824185739974537.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824185740301917.png)
(2)加速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824185740582922.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824185740847622.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824185741159546.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824185741643912.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824185741939420.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824185742205749.png)
点评:关键是知道恒定功率启动时,加速度在变化,牵引力在增大,当牵引力等于阻力时,速度最大,
恒定牵引力启动时,加速度恒定,当功率达到额定功率时,速度最大,
![](http://thumb2018.1010pic.com/images/loading.gif)
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