Question

Standing from the top of a platform. Frank

Answer 1

Answer:

7.5 seconds.

Step-by-step explanation:

The height of the arrow as a function of time t is given by :

$h = -16t^2 + 118t + 15$

Here, 118 ft/s is the initial velocity and 15 feet is the height of the platform. We need to find How many seconds will take the arrow to reach the  ground. When it reaches the ground, h(t) = 0

$-16t^2 + 118t + 15=0$

The above is a quadratic equation. The solution of the above equation is given by :

$x=\dfrac{-b\pm \sqrt{b^2-4ac} }{2a}$

Here, b = 118, a = -16 and c = 15

So,

$t=\dfrac{-118\pm \sqrt{(118)^2-4(-16)(15)} }{2\times (-16)}\\\\t=-0.125\ \text{and}\ 7.5\ s$

Time can't be negative.

So, it will take 7.5 seconds to reach the ground.