Mechanical toy cars A, B, and C, each traveling at its own uniform rate, started

游客2025-02-24 47

问题 Mechanical toy cars A, B, and C, each traveling at its own uniform rate, started from the same point at the same time and raced a 400-meter course. When A crossed the finish line. B was 40 meters behind A, and C was 58 meters behind A. When B crossed the finish line, how many meters was C from the finish line?

选项 A、16
B、18
C、19
D、20
E、22

答案 D

解析机械玩具车A、B和C在同一时间、同一地点出发，各自以均匀的速度参加400米比赛。当A越过终点线时，B车落后A车40米，C车落后A车58米，问当B车越过终点线时，C车离终点线还有多远?
解：本题的正确答案为(D)。此题是一道极易被考生做错的题。大多数考生都这样认为：当A到终点时，B和C相差(58-40)=18米，由于B和C都是匀速行驶的，所以B车到终点时，两者的距离保持不变，仍为18米。而实际上，因为B和C两车的运动速度不同，所以在最后的40米，B和C两车之间的距离会加大。B和C匀速运动，在前360米相差了18米，设在最后的40米B和C相差的距离将增大x，则根据题意可列出下面的方程：18/360 = x/40 → x=2；所以B车越过终点时，C车距中点还有18+2=20米。

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