A hang glider dropped his cell phone from a height of 350 feet. How many seconds did it take for the cell phone to reach the ground?

Question

how many seconds did it take?

Answer 1

If you ignore air resistance, set the vertical fall distance equal to gt²/2 and solve for t.

 

h = 350 ft

g = 32 ft/s²

 

h = gt²/2

 

t = √(2h/g)

 

Plug in h and g, and get t in seconds.  You can finish from here.

Answer 2

Knowing that the position function of a free-falling object is represented by the equation s(t)=(1/2)gt²+v₀t+s₀ where

g=acceleration due to gravity, which is approximately -32ft/sec²

t=time

v₀=initial velocity of the object. In our case v₀=0

s₀=initial height of the object. In our case s₀=350ft

We want to solve for t when s(t)=0:

0=(1/2)(-32)t²+(0)t+350

0=-16t²+350

16t²=350

t²=350/16

t²=21.875

t=±4.677sec

Because time cannot be negative, the answer is approximately 4.68 seconds.