Question

PLEASE HELP ASAP!!! FULL ANSWER!!!

A person standing close to the edge on top of a 40-foot building throws a ball vertically upward. The quadratic function h = − 16t^2 + 72t + 40 models the ball's height above the ground, h , in feet, t seconds after it was thrown.

a) What is the maximum height of the ball? _____________ feet

b) How many seconds does it take until the ball hits the ground? _____________ seconds

Answer 1

a) 121 feet ; b) 5 seconds

Explanation:

maximum height = y coordinare of vertex

x coordinate = -72/2 * -16

-72/-32 = 9/4 = 2.25

y coordinate =

-16(2.25)^2 + 72(2.25) + 40

-81 + 162 + 40

-81 + 202 = 121 feet

The ball hits the ground when y = 0

-16t^2 + 72t + 40 = 0

-2t^2 + 9t + 5 = 0

discriminant = 81 -4 (-2 * 5) = 81 -4(-10) = 81 + 40 = 121

We are searching only positive value

t = (-9 -11)/-4 = -20/-4 = 5 seconds