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When a baseball is hit by a batter, the height of the ball, h(t), at time t, t=0 is determined by the equation h(t)=-16t^2+64t^2+4. If t is in seconds, for which interval of time is the height of the ball greater than or equal to 52 feet?

A: 1
B: t<=1

C: 0
D: 1<=t<=3

Verified Answer :

Let

t--------> the time in seconds

h--------> the height of the ball in feet

we know that

\(h(t)=-16t^2+64t^2+4\)

Using a graphing tool

see the attached figure

The height of the ball is greater than or equal to \(52\) feet for

\(t\geq 1\ sec\)

therefore

the answer is the option D

\(1\ sec \leq t \leq 3\ sec\)

View image calculista

The correct option is \(\boxed{\bf\ option D}\) i.e., \(\boxed{1\leq t\leq 3}\).

Further explanation:

Given:

The height of the ball is determined by the equation \(h(t)=-16t^{2}+64t^{2}+4\).

Calculation:

Consider \(t\) as the interval of time and \(h\) as the height of the time.

The equation is given as follows:

\(\boxed{h(t)=-16t^{2}+64t^{2}+4}\)

Further solve the above equation as follows:

\(\begin{aligned}h(t)&=-16t^{2}+64t^{2}+4\\&=48t^{2}+4\end{aligned}\)

We have to check the interval in which height of the ball is greater than or equal to \(52\text{ feet}\).

Check the option A by substituting \(t=1\) in the equation \(h(t)=-16t^{2}+64t^{2}+4\) as follows:

\(\begin{aligned}h(1)&=48\cdot (1)^{2}+4\\&=18+4\\&=52\end{aligned}\)

The height of the ball is \(52\text{ feet}\) at \(t=1\).

The option A is not full filling the condition completely as the height is not greater than \(52\text{ feet}\).

This implies that option A is incorrect.

Now, move to the option B that is \(t\leq 1\).

Check the second option by substituting \(t=0\) in the equation \(h(t)=48t^{2}+4\) as follows:

\(\begin{aligned}h(0)&=48\cdot (0)^{2}+4\\&=0+4\\&=4\end{aligned}\)  

The height of the ball is \(4\text{ feet}\) at time \(t=0\).

The inequality for time \(t\leq 1\) is not satisfying the condition.

Therefore, option B is incorrect.

Now check for the option C that is \(t=0\) but we have already discarded this option in option B.

So, there is no need to check the option C.

Therefore, check the last option D that is the interval of time \(1\leq t\leq 3\).

The height of the ball is \(52\text{ feet}\) at time \(t=1\) as we already calculated for the option A.

Now substitute \(t=3\) in the given equation  to check the interval \(1\leq t\leq 3\).

\(\begin{aligned}h(3)&=48\cdot (3)^{2}+4\\&=(48\cdot 9)+4\\&=436\end{aligned}\)  

The height of the ball is \(436\text{ feet}\) at time \(t=3\) satisfies the condition completely as the height \(436\text{ feet}\) is greater than \(52\text{ feet}\).

Therefore, the boundary points of the interval \(1\leq t\leq 3\) satisfy the condition.

Now check another point which lies in the interval of time \(1\leq t\leq 3\).

So, substitute \(t=2\) in the equation \(h(t)=48t^{2}+4\).

\(\begin{aligned}h(2)&=48\cdot (2)^{2}+4\\&=(48\cdot 4)+4\\&=196\end{aligned}\)  

The height of the ball is \(196\text{ feet}\) at time \(t=2\) satisfies the condition completely as the height \(196\text{ feet}\) is greater than \(52\text{ feet}\).

Therefore, the height of the ball is greater than or equal to \(52\text{ feet}\) in the interval of time \(1\leq t\leq 3\).

Thus, the correct option is \(\boxed{\bf option D}\).

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Answer details:

Grade: High school

Subject: Mathematics

Chapter: Quadratic equations

Keywords: Polynomial, quadratic equation, substitution, baseball, interval, height, greater than, equation, time, seconds, simplification, solution, inequality.