NASA creates a weightless
environment by flying a plane in a series of
parabolic paths. The height h (in feet) of a plane
after t seconds in a parabolic flight path can be
modeled by the graph of h = -11t+ + 700t + 21,000.
The passengers experience a weightless environment
when the height of the plane is greater than or equal
to 30,800 feet. Find the period of weightlessness on such
a flight. Explain.