Johnny left point A, walking North at a steady velocity V km/h . At the moment that he was at a distance of 6 km from A, a biker Tom left A to bring Johnny back, his speed being 9 km/h higher than Johnny's.
When they met they turned back and travelled South at 4 km/h.

For what value of V the duration of Johnny's trip would be minimal?

Via slightly different algebra, same calculus (after all Newton is Newton!) I arrived at the same answer as Charlie - V=6km/hr minimizes the total time for the round trip.

Posted by Kenny M on 2011-11-25 10:54:11