题目内容
(10分) 汽车前方120m有一自行车正以6m/s的速度匀速前进,汽车以18m/s的速度追赶自行车,若两车在同一条公路不同车道上作同方向的直线运动,求:
(1)经多长时间,两车第一次相遇?
(2)若汽车追上自行车后立即刹车,汽车刹车过程中的加速度大小为2m/s2,则再经多长时间两车第二次相遇?
(1)经多长时间,两车第一次相遇?
(2)若汽车追上自行车后立即刹车,汽车刹车过程中的加速度大小为2m/s2,则再经多长时间两车第二次相遇?
(1)
(2)13.5s
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652572441.png)
试题分析:(1)设自行车速度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652588618.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652604654.png)
相距
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652619561.png)
设经t两车相遇,应有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652635554.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652572441.png)
(2)设汽车刹车后经
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652666319.png)
则:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652682590.png)
即
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652697733.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652713477.png)
在
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652666319.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652760720.png)
汽车前进
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652775875.png)
因
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652791411.png)
则自行车还需追及时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652806766.png)
则从第一次相遇起还需
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002652822721.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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