College

Jerald jumped from a bungee tower. If the equation that models his height, in feet, is [tex]h=-16t^2+729[/tex], where [tex]t[/tex] is the time in seconds, for which interval of time is he less than 104 feet above the ground?

A. [tex]t \ \textgreater \ 6.25[/tex]

B. [tex]-6.25 \ \textless \ t \ \textless \ 6.25[/tex]

C. [tex]t \ \textless \ 6.25[/tex]

D. [tex]0 \leq t \leq 6.25[/tex]

Answer :

Let's solve the problem and determine the time interval where Jerald is less than 104 feet above the ground.

The equation given for Jerald's height is:
[tex]\[ h = -16t^2 + 729 \][/tex]
where [tex]\( h \)[/tex] is Jerald's height in feet and [tex]\( t \)[/tex] is the time in seconds.

We want to find the time intervals when Jerald's height is less than 104 feet. So, we set up the inequality:
[tex]\[ -16t^2 + 729 < 104 \][/tex]

First, solve this inequality for [tex]\( t \)[/tex].

1. Subtract 104 from both sides:
[tex]\[ -16t^2 + 729 - 104 < 0 \][/tex]

2. Simplify the equation:
[tex]\[ -16t^2 + 625 < 0 \][/tex]

3. Rearrange the terms:
[tex]\[ 16t^2 > 625 \][/tex]

4. Divide by 16:
[tex]\[ t^2 > \frac{625}{16} \][/tex]

5. Calculate [tex]\( \frac{625}{16} \)[/tex]:
[tex]\[ t^2 > 39.0625 \][/tex]

6. Take the square root of both sides to solve for [tex]\( t \)[/tex]:
[tex]\[ t > \sqrt{39.0625} \quad \text{or} \quad t < -\sqrt{39.0625} \][/tex]

7. Calculate the square root:
[tex]\[ t > 6.25 \quad \text{or} \quad t < -6.25 \][/tex]

Since time ([tex]\( t \)[/tex]) cannot be a negative value (because Jerald couldn't have jumped before [tex]\( t = 0 \)[/tex]), we consider only positive [tex]\( t \)[/tex]. So, the solution is:

[tex]\[ t > 6.25 \][/tex]

Therefore, the interval for which Jerald is less than 104 feet above the ground is: [tex]\( t > 6.25 \)[/tex].