SOLUTION: A ball is thrown from the top of a building from a height of 75 feet above the ground. The height of the ball, H, in feet from the ground, and time, t, in seconds, can be modeled

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equation Customizable Word Problems -> SOLUTION: A ball is thrown from the top of a building from a height of 75 feet above the ground. The height of the ball, H, in feet from the ground, and time, t, in seconds, can be modeled      Log On


   

Question 1205874: A ball is thrown from the top of a building from a height of 75 feet
above the ground. The height of the ball, H, in feet from the
ground, and time, t, in seconds, can be modeled by the equation
H = −5(t−3)(t+5).
Select the true statement.
Ⓐ The ball reaches the ground in 3 seconds.
Ⓑ The ball reaches the ground in 5 seconds.
Ⓒ The ball reaches the ground in 15 seconds.
Ⓓ The ball reaches the ground in 25 seconds.
Found 2 solutions by MathLover1, ikleyn:
Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!

H+=+-5%28t-3%29%28t%2B5%29
Set H=0 for ground height, then solve for+t
0=+-5%28t-3%29%28t%2B5%29
if 0=+%28t-3%29=> t=3
if 0=+%28t%2B5%29=> t=-5+=>negative zero is not meaningful in this situation, so disregard it
answer:
Ⓐ The ball reaches the ground in 3 seconds.

Answer by ikleyn(52754) About Me  (Show Source):
You can put this solution on YOUR website!
.

This equation in your post for height,   H(t) = -5(*-3)*(t+5),   does not work in feet,

because its leading coefficient at  t^2  is  -5  ft/s^2.


A correct equation for height in feet has the leading coefficient  -16  ft/s^2  at  t^2.


When a person comes and claims that the height equation for a projectile has the form as it is written in your post,
it becomes clear that this person does not know the basics of  Physics (kinematics),  as well as the relevant part of  Algebra.