U = 0, initial vertical velocity
v = 60 mph = 88 ft/s
Ignore air resistance and take g = 32 ft/s².
It t = time to attain 60 mph, then
(88 ft/s) = (32 ft/s²)*(t s)
t = 88/32 = 2.75 s
Answer: 2.75 s
Because the strength of the gravitational forces between two objects
depends on the distance between the objects' centers, and when your
elevation changes, so does the distance between your center and the
center of the Earth.