An object is thrown upward from a height of 480 feet with an initial velocity of 16 feet per second. The height h (in feet)of the object after t seconds is modeled in the equation $h = - 16 t ^ { 2 } + 16 t + 480$ . How long will it take for the object to reach the ground?
A)5 seconds
B)6 seconds
C)1 second
D)3 seconds
E)2 seconds

Question

Quizplus · Accepted Answer

When the object reaches the ground, its height h is equal to zero.
So we need to solve the equation 
0 = -16t^2 + 16t + 480
Dividing both sides by -16, we get
t^2 - t - 30 = 0
Factoring the left side, we get
(t - 6)(t + 5) = 0
Thus, t = 6 or t = -5.
Since time cannot be negative, the answer is t = 6 seconds.

An Object Is Thrown Upward from a Height of 480 h=−16t2+16t+480h = - 16 t ^ { 2 } + 16 t + 480h=−16t2+16t+480

An Object Is Thrown Upward from a Height of 480 $h = - 16 t ^ { 2 } + 16 t + 480$