180: Day 20: “One train leave a station at 2:30, and another train leaves…

Here’s a classic physics problem:

One train leaves a station at 2:30 at a speed of 40 m/s,
and a second train leaves another station at 50 m/s.
The stations are 40 km apart, and the trains are heading
toward each other. At what time and position will the
trains collide?

These days, many teachers use this as a chance for an actual experiment. I challenge my students to determine the speed of their cars, then I match them up with a random group (well I know each group has a car with a different speed). They then need to calculate the position the cars will collide if they start four meters apart. I have a grade sheet that shows them their grade. My standard sheet has A-D on it, with A at the center where the cars are due to collide.

With each buggies traveling 1.2-3.8 meters, I probably should give them a bit more slack in the “A” range, so I’m thinking that for next year I may use three sheets of paper with most of the center one being the “A”, and the outside ones being B-D.

I like this lab because it’s easy to get correct predictions, and students have to go back and check their math if they don’t get an “A”.

Here’s a video showing an accurate prediction. The class, and I, get quite excited as the collision moment approaches!

One Reply to “180: Day 20: “One train leave a station at 2:30, and another train leaves…”

How did the students receive this experiment? Were they able to gain a deeper understanding of the physics problem? Was this given before the actual problem or after? What were you looking for after they ran the experiment?

How did the students receive this experiment? Were they able to gain a deeper understanding of the physics problem? Was this given before the actual problem or after? What were you looking for after they ran the experiment?