# Math

Evaluate a Quadratic Function Given an Output

Here you will find the input for a quadratic function when the output is given.

1. A ball is drop from the top of a building. The height, h, of the ball above ground after t seconds can be calculated using the formula
h(t) = -16t2 + 400

How many seconds will it take for the ball to hit the ground?

Hint: The ball will hit the ground when the height above ground is 0; that is, when h(t) = 0.
My answer is 400 because h(0)=-16t+400 but i keep getteng it wrong

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1. you do not want h(0) -- that is the initial height (time t=0)

You want t when h=0. That is,

-16t^2 + 400 = 0
t^2 = 25
t = 5

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2. ok, then according to their hint,

0 = -16t^2 + 400
16t^2 = 400
t^2= 400/16 = 25
t = √25 = 5

so it took 5 seconds

How could it possible take 400 seconds or almost 7 minutes for a ball to fall from 400 ft ???

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