Question

1) The height, h, in feet of a ball above the ground is given by h = -16t2 + 64t+ 80, where t is the time in seconds. How long does it take the ball to hit the ground? es A) 3 seconds B) 4 seconds 95 seconds D) 6 seconds​

Answer 1

C) 5 seconds

Explanation:

`h = - 16t {}^(2) + 64t + 80`

When the ball hits the ground, the height is 0.

`0 = - 16t {}^(2) + 64t + 80`

Factor out the greatest common factor: 16

`0 = - 16(t {}^(2) - 4t - 5)`

Find numbers whose sum is -5 and product is - 4.

Those numbers are - 5 and 1: - 5 × 1 = - 5, - 5 + 1 = - 4

`0 = - 16(t - 5)(t + 1)`

`t - 5 = 0`

Or

`t + 1 = 0`

So,

`t = 5`

Or

`t = - 1`

Since time cannot be a negative value the correct answer is 5 seconds.