The initial height above ground is 1800 ft.
The height (ft) above ground at time t seconds is
h(t) = 1800 - 16t²
Part a.
If the parachute opens when h = 1000 ft, then
1000 = 1800 - 16t²
16t² = 18000 - 1000 = 17000
t² = 17000/16
Answer: t = 32.60 s
Part b.
If the parachute opens when h = 950 ft, then
16t² = 18000 -950 = 17050
t² = 17050/16
Answer: t = 32.64 s
Part c.
It is not reasonable for the parachute to open at less than 500 ft from the ground, else the parachutist may suffer landing harm.
If h = 500, then
16t² = 18000 - 500 = 17500
t = 33.07 s
If h = 18000, then
t² = 18000/16
t = 33.54 s
Answer:
A reasonable domain for h is t =(33.07, 33.54) s.
A reasonable range for h is (500, 18000) ft.