Question 137005
If an object is thrown upward with an initial velocity of 64 ft/sec, its height after t sec is given by h = 64t - 16t^2. Find the number of seconds the object is in the air before it hits the ground.
:
When the ball hits the ground, h = 0
-16t^2 + 64t = 0
Factor out -16t
-16t(t - 4) = 0
:
t = 0
and 
t = 4 seconds for the object to hit the ground
:
:
Substitute 4 for t in the original equation to check it:
-16(4^2) + 64(4) =
-256 + 256 = 0