TRAVEL PROBLEM
Travel problems, meeting & catch-up.
Random meeting and catch-up problems asking for time or distance, with formula steps and a live animation of the motion.
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Solution animation · the motion
t = 0 h: A has gone 0 km, B 0 km — together 0 km, still 520 km apart.
What is this?
Travel problems study motion with distance = speed × time. Meeting: two travelers move toward each other, so time = distance ÷ (v₁ + v₂). Catch-up: same direction, so time = gap ÷ (v₁ − v₂). Press Play: the vehicles move and the gap shrinks at the speed-sum / speed-diff rate until they meet — the formula becomes something you can see, not memorize.
示例与注意事项Example & notes
一个例子A worked example
甲 60 km/h、乙 40 km/h 相向而行，相距 200 km：速度和 100 km/h，2 小时后相遇。Two travellers at 60 and 40 km/h approach each other from 200 km apart: combined speed 100 km/h, meeting after 2 hours.
注意事项Things to watch
- 相遇看「速度和」，追及看「速度差」，搞反会全盘算错。Approach problems use the sum of speeds; catch-up problems use the difference — swapping them ruins everything.
- 单位要统一，分钟与小时混用是最常见的失分点。Unify units — mixing minutes and hours is the classic error.
- 往返平均速度是总路程除以总时间，不是两个速度的平均值。Average speed for a round trip is total distance over total time, not the mean of the two speeds.
相关问答More Q&A
能只求距离吗？Can it solve for distance only?
可以，输入时间与速度即得距离，也可反求时间。Yes — give time and speed to get distance, or solve for time instead.
有动画演示吗？Is there an animation?
有，两车运动与剩余距离会动态展示，便于讲清"为什么除以速度和"。Yes — movement and remaining distance update live, which explains the division.