Question

How long will it take until the driver enters the water? Also how do you know?

Answer 1

Given:

h= -t^2 + 8t + 115

Where:

h = height

When the diver enters the water , h= 0

0 = -t^2 + 8t + 115

a = -1

b= 8

c= 115

Apply quadratic equation:

$\frac{-b\pm\sqrt[\placeholder{⬚}]{b^2-4ac}}{2a}$

Replacing:

$\frac{-8\pm\sqrt[\placeholder{⬚}]{8^2-4(-1)(115)}}{2(-1)}$$\frac{-8\pm\sqrt[\placeholder{⬚}]{524}}{-2}$

negative:

$\frac{-8-\sqrt[]{524}}{-2}=15.45$

positive

$\frac{-8+\sqrt[\placeholder{⬚}]{524}}{-2}=-7.44$

Answer:

t = 15.45 s