The height of a golf ball is given by
[tex]\[ f(t) = -16t^2 + 40t + 3.6 \][/tex]
where [tex]\( f(t) \)[/tex] represents the height of the golf ball in feet, and [tex]\( t \)[/tex] is the number of seconds that has elapsed. Round all values to three decimal places.

A) Find [tex]\( f(0) = \square \)[/tex] feet
B) Find [tex]\( f(2) = \square \)[/tex] feet
C) Find the time it takes for the golf ball to reach its maximum height.
[tex]\[ \square \][/tex] seconds
D) What is the maximum height?
[tex]\[ \square \][/tex] feet
E) When will the golf ball hit the ground?
[tex]\[ \square \][/tex] seconds
F) When will the golf ball be 15 feet above the ground? Write your answers as a list, with your answers separated by commas.
[tex]\[ \square \][/tex] seconds



Answer :

Let's break down each of the parts step by step.

### Part A: Find [tex]\( f(0) \)[/tex].
To find [tex]\( f(0) \)[/tex], substitute [tex]\( t = 0 \)[/tex] into the equation:

[tex]\[ f(t) = -16t^2 + 40t + 3.6 \][/tex]

[tex]\[ f(0) = -16(0)^2 + 40(0) + 3.6 = 3.6 \][/tex]

So,
[tex]\[ f(0) = 3.6 \text{ feet} \][/tex]

### Part B: Find [tex]\( f(2) \)[/tex].
To find [tex]\( f(2) \)[/tex], substitute [tex]\( t = 2 \)[/tex] into the equation:

[tex]\[ f(t) = -16t^2 + 40t + 3.6 \][/tex]

[tex]\[ f(2) = -16(2)^2 + 40(2) + 3.6 = -64 + 80 + 3.6 = 19.6 \][/tex]

So,
[tex]\[ f(2) = 19.6 \text{ feet} \][/tex]

### Part C: Find the time it takes for the golf ball to reach its maximum height.
The time at which a quadratic function [tex]\( at^2 + bt + c \)[/tex] reaches its maximum or minimum is given by [tex]\( t = -\frac{b}{2a} \)[/tex].

Here, [tex]\( a = -16 \)[/tex] and [tex]\( b = 40 \)[/tex].

[tex]\[ t = -\frac{40}{2 \cdot -16} = \frac{40}{32} = 1.25 \][/tex]

So, the golf ball reaches its maximum height at
[tex]\[ t = 1.25 \text{ seconds} \][/tex]

### Part D: What is the maximum height?
To find the maximum height, substitute [tex]\( t = 1.25 \)[/tex] into the height function:

[tex]\[ f(t) = -16t^2 + 40t + 3.6 \][/tex]

[tex]\[ f(1.25) = -16(1.25)^2 + 40(1.25) + 3.6 = -16(1.5625) + 50 + 3.6 = 28.6 \][/tex]

So, the maximum height is
[tex]\[ 28.6 \text{ feet} \][/tex]

### Part E: When will the golf ball hit the ground?
The golf ball hits the ground when [tex]\( f(t) = 0 \)[/tex]:

[tex]\[ -16t^2 + 40t + 3.6 = 0 \][/tex]

Solving this quadratic equation, we get a positive root of

[tex]\[ t = 2.587 \][/tex]

So, the golf ball hits the ground at
[tex]\[ t = 2.587 \text{ seconds} \][/tex]

### Part F: When will the golf ball be 15 feet above the ground?
To find when the golf ball is 15 feet above the ground, solve [tex]\( f(t) = 15 \)[/tex]:

[tex]\[ -16t^2 + 40t + 3.6 = 15 \][/tex]

Simplifying gives:

[tex]\[ -16t^2 + 40t - 11.4 = 0 \][/tex]

Solving this quadratic equation, the positive solutions are

[tex]\[ t = 0.328 \text{ seconds}, \quad t = 2.172 \text{ seconds} \][/tex]

So, the times when the golf ball is 15 feet above the ground are
[tex]\[ 0.328 \text{ seconds}, 2.172 \text{ seconds} \][/tex]

By combining all the results, we get:

A) [tex]\( f(0) = 3.6 \text{ feet} \)[/tex]

B) [tex]\( f(2) = 19.6 \text{ feet} \)[/tex]

C) Time to maximum height: [tex]\( 1.25 \text{ seconds} \)[/tex]

D) Maximum height: [tex]\( 28.6 \text{ feet} \)[/tex]

E) Time when the golf ball hits the ground: [tex]\( 2.587 \text{ seconds} \)[/tex]

F) Times when the golf ball is 15 feet above the ground: [tex]\( 0.328 \text{ seconds}, 2.172 \text{ seconds} \)[/tex]