Calculating f.p.s. and m.p.h.

Miles per hour to feet per second

To convert m.p.h. to f.p.s., you simply reverse the process.  Divide the m.p.h. by two and then multiply that answer by three.

Feet per second to miles per hour.

The quickest way to convert f.p.s.  to m.p.h. is to divide the f.p.s. by three and then multiply that answer by two.  The answer will be close enough for all practical purposes.