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On September 28th, 20 13, Taohuayu Yellow River Highway Bridge in Zhengzhou was completed and opened to traffic, which is a part of Zhengzhou-Jiaozuo Yuntai Mountain Scenic Area.
B

Test and analysis: within the reaction time of people, the car moves at a uniform speed and then decelerates at a uniform speed. Let the initial speed be V, and before the speed is reduced to 0, the displacement of the trolley is x=30m, then it is correct to have vt+v 2 /2a=x, v= 15m/s, and B.