If an object is propelled upward from a height of 144 feet at an initial velocity of 128 feet per second, then its height after t seconds is given by the equation $h ( t ) = - 16 t ^ { 2 } + 128 t + 144$ After how many seconds does the object
Hit the ground?
A) 9 sec
B) 8.0 sec
C) 11 sec
D) 4.5 sec

Question

Quizplus · Accepted Answer

To find when the object hits the ground, set $h(t) = 0$ and solve for $t$. The equation becomes $0 = -16t^2 + 128t + 144$. Factoring or using the quadratic formula, we find that $t = 9$ seconds is the positive solution that represents the time when the object hits the ground.

If an Object Is Propelled Upward from a Height of 144