You are travelling to point B from point A at a speed of 30mph. You travel back to point A from Point B (taking the same route) at 60mph. What is your average speed?

If the speed going is a, and the speed returning is b, then the overall average speed is 2/((1/a)+(1/b))=harmonic mean of a and b. So the harmonic mean which was encountered in Tristan's recent problem does appear in a physical context.

Posted by Richard on 2006-10-30 14:10:12