Word Question

Question

I'm having trouble understanding how to plug everything in on this one. I need some help please

 

The height of an object thrown downward with a velocity of 32 ft/sec from the roof of a 128 feet tall building is modeled by

 

h(t) = -16t^2 - 32t + 128

Here, h is the height of the object off the ground (in feet), t seconds after the object is thrown.

 

a. How long does it take before the object hits the ground?

Answer 1

When the object hits the ground, its height is zero. So, plug in h(t) = 0, then solve for t:

 

0 = -16t^2 - 32t + 128 = t^2 + 2t - 8

t(t + 2) = 8

t = 2

 

It will take 2 seconds before the object hits the ground.