Pinewood Derby Debacle

May 01, 2021

RAY: This is a quasi-automotive puzzler, sent in by John Whittier. He writes;

"This is the season for Cub Scouts all over the country to hold their Pinewood Derby Races. My two sons built their cars and wanted to compete against each other at home prior to the real race. I built a simple racetrack using materials I had on hand.

However, I only had materials to build a one-lane track. I had planned to run the cars individually and use a stopwatch to time each car. So, son A would put his car at the top and let it go. I'd start the watch, and when it got across the finish line, I'd check the time. 

But when we attempted to hold races I discovered that the cars traversed my very short track in such a short time that I could not start and stop the watch fast enough to accurately measure the times such that we could really determine which car was faster.

My younger son, who was eight years old, came up with a solution. Remember, all we had were the two cars, the short test track, the stopwatch, and the three of us.

What solution did he come up with?"


RAY: He very simply said, "Let's put both cars on the track, one behind the other."

If the front car, that is the car closest to the finish line is faster when we release the two cars simultaneously, of course, that one will pull away from the other one, and it will be the faster car.

Otherwise, the other one will push it over the finish line.

Once you've done that first heat, you're going to reverse the cars' position and see if in fact that no gap opens and then the rear car, which had been the front car, will be the faster car.

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