Two cyclists toward each other: when do they meet
A motion problem with sliders: change the distance and speeds, run the scene and check your answer. A model for building your own problems.
2D
Age 10+10 min
Motion problems
Loading simulation…
Press “Run”. Bodies move by the laws of physics: gravity, friction, elasticity.
What the experiment shows
Two cyclists leave two villages at the same time and ride toward each other. The distance and speeds are sliders, the captions compute the current gap, and a rule shows the moment they meet. The Task panel checks the answer and shows the solution.
How to run it
- Run the scene and watch the “Gap” caption: the distance shrinks steadily.
- Enter your answer in the Task panel and press “Check”.
- Move the speed and distance sliders and solve again: the statement updates itself.
Questions to discuss
- Why are the speeds added when moving toward each other?
- How does the meeting time change if the distance doubles?
The science
Every hour the gap shrinks by the sum of the speeds: the closing speed. The meeting time is the distance divided by the closing speed: t = S / (v₁ + v₂).
Try it at home
Mark two points 20 steps apart on the pavement and walk toward each other with a friend, comparing how many steps each took.
What to change in the editor
- Open the example in the editor and replace the cyclists with pedestrians, changing the speed scale.
- Add a “delay” variable and let the second one leave later to get a catch-up problem.