Question

The pep squad at the local college basketball game launches T-shirts into the crowd using a cannon that is placed on the floor and stands 2 feet high. The cannon fires shirts with an upward velocity of 38 feet per second. Using the function h=−16t2+38t
, which of the following correctly identifies the intercepts and the vertex and correctly explains the path of the shirts?(1 point)
Responses

(0,0)
(1.19,22.56)
and (0,2.38)
; After being launched from the ground, the shirts will reach a height of 1.19
feet in 24.56
seconds before returning to ground level after 2.38
seconds.
left parenthesis 0 comma 0 right parenthesis open paren 1 point 1 9 comma 22 point 5 6 close parenand left parenthesis 0 comma 2.38 right parenthesis ; After being launched from the ground, the shirts will reach a height of 1 point 1 9 feet in 24 point 5 6 seconds before returning to ground level after 2 point 3 8 seconds.

(1.19,24.56)
and (2.38,0)
; After being launched from the ground, the shirts will return to ground level after 2.38
seconds.
left parenthesis 1.19 comma 22.56 right parenthesis and left parenthesis 2.38 comma 0 right parenthesis ; After being launched from the ground, the shirts will return to ground level after 2 point 3 8 seconds.

(2.38,0)
; After being launched from the ground, the shirts will return to ground level after 2.38
seconds.
left parenthesis 2.38 comma 0 right parenthesis ; After being launched from the ground, the shirts will return to ground level after 2 point 3 8 seconds.

(0,2)
, (1.19,24.56)
, and (2.38,0)
; After being launched from the cannon at a height of 2 feet, the shirts reach the height of 24.56
feet after 1.19
seconds before returning to ground level after 2.38
seconds.
open paren 0 comma 2 close paren, open paren 1 point 1 9 comma 24 point 5 6 close paren, and open paren 2 point 3 8 comma 0 close paren; After being launched from the cannon at a height of 2 feet, the shirts reach the height of 24 point 5 6 feet after 1 point 1 9 seconds before returning to ground level after 2 point 3 8 seconds.
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1 answer

To analyze the motion of the shirts launched from the cannon, we can look at the function given:

\[ h(t) = -16t^2 + 38t + 2 \]

where \( h(t) \) is the height in feet after \( t \) seconds, given that the cannon starts at a height of 2 feet.

1. Finding the intercepts:

  • To find the ground level (when height = 0):

\[ 0 = -16t^2 + 38t + 2 \]

Using the quadratic formula:

\[ t = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]

Here, \( a = -16 \), \( b = 38 \), and \( c = 2 \).

Calculating the discriminant:

\[ b^2 - 4ac = 38^2 - 4(-16)(2) = 1444 + 128 = 1572 \]

Now using the quadratic formula:

\[ t = \frac{-38 \pm \sqrt{1572}}{2(-16)} \]

Calculating \( \sqrt{1572} \approx 39.6 \):

\[ t = \frac{-38 \pm 39.6}{-32} \]

Two possible solutions:

  1. \( t \approx \frac{-38 + 39.6}{-32} \Rightarrow t \approx 0.049 \) seconds
  2. \( t \approx \frac{-38 - 39.6}{-32} \Rightarrow t \approx 2.38 \) seconds

So the intercepts are approximately \( (0, 2) \) and \( (2.38, 0) \).

2. Finding the vertex:

The vertex of a parabola given by \( h(t) \) can be found using the formula \( t = -\frac{b}{2a} \):

\[ t = -\frac{38}{2 \times -16} = \frac{38}{32} = 1.19 \text{ seconds} \]

Now calculate the height at the vertex:

\[ h(1.19) = -16(1.19)^2 + 38(1.19) + 2 \] \[ = -16(1.4161) + 45.62 + 2 \] \[ \approx -22.66 + 45.62 + 2 \approx 24.96 \text{ feet} \]

So the vertex is around \( (1.19, 24.96) \).

3. Summary of findings:

  • Intercepts: \( (0, 2) \) and \( (2.38, 0) \)
  • Vertex: \( (1.19, 24.96) \)

4. Interpreting the results:

The shirts are launched from a height of 2 feet. After about 1.19 seconds, they reach their maximum height of approximately 24.96 feet. Then, they descend back to ground level after approximately 2.38 seconds.

Conclusion:

The correct response to fit these findings about the intercepts and the path of the shirts is:

(0, 2), (1.19, 24.96), and (2.38, 0); After being launched from the cannon at a height of 2 feet, the shirts reach the height of 24.96 feet after 1.19 seconds before returning to ground level after 2.38 seconds.

Since this option includes the important context of starting from 2 feet, maximally reaching 24.96 feet at 1.19 seconds, and returning to ground level at 2.38 seconds, it correctly summarizes the situation.