Which wave requires a physical medium through which to travel?

All mechanical waves require a physical medium through which to travel.  If there isn't any, then mechanical waves don't travel.

Mechanical waves are the waves where physical particles are doing the waving.  They include sound waves, ocean waves, ripples on a pond, clarinet waves, Slinky waves, guitar-string waves, rope waves, etc.  

what is the speed of a softball that travels 20m in 2secs

speed = 20/2 = 10 m/s