2. 外语
  3. 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

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

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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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