But yes, we are back with a new brain teaser each Saturday to
Here in Menlo Park, California, despite it nearing Halloween, the weather is still beautiful. This past Thursday morning, we did what we do every Thursday morning when it's not raining (i.e., every Thursday): we played ultimate frisbee at the park. We play with a fairly standard disc that weighs 175 grams and is 27.3 cm across.
Now super-stud-player Alonzo has a wicked forehand that sends the disc spinning at 3.2 rotations per second with sniper-worthy accuracy. On this day, a poor ant hitched a ride on the disc just as Alonzo sent it flying. It was on the very edge of the disc and cruising along at 4cm/sec. How long does it take for the ant to crawl all the way around if the disc is spinning counter-clockwise and the ant is walking clockwise?
Ready for the answer?
Did I tell you the disc was red? As red as a herring.
Almost none of information in the teaser matters. The fact that the disc is spinning has nothing to do with the time it takes the ant to walk around because the ant is going along with the spin. So it's really just the time it takes for the ant to walk in a circle with diameter 27.3cm. The disc has a circumference of 27.3 x π ~= 85.76cm, so the ant takes about 21.44 seconds to walk around it.