Alan and Brianna are driving their cars along the same straight road with the constant velocities of 33 mph and 63 mph, respectively. Their friend Chris is driving along a different straight road at the constant velocity of 52 mph. (All these velocities are measured relative to Earth.)

During the motion, the distance between Chris and Alan always remains equal to that between Chris and Brianna. Find Chris’s speed relative to Brianna.

The March, April, and May issues of Challenges attracted many submissions from all over the world, marking a great finish of the 2020/21 “season.”

We are pleased to recognize the following contributors:

Guidelines for contributors

Many thanks to all contributors and we hope to hear from many more of you this year!

Note: we always welcome and appreciate reader-contributed original Challenges!

The solutions to the past Challenges can be found here:

Please note that AAPT membership may...

AAPT members receive access to The Physics Teacher and the American Journal of Physics as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.