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If a toy rocket is launched vertically upward from ground level with an initial velocity of 128 feet per second, its height [tex] h [/tex] after [tex] t [/tex] seconds is given by the equation [tex] h(t) = -16t^2 + 128t [/tex] (air resistance is neglected).

a. How long will it take the rocket to reach its maximum height?

b. What is the maximum height?

c. How long will it take for the rocket to reach the ground?

Answer :

Sure! Let's solve the problem step-by-step.

We have the height of a toy rocket given by the equation:
[tex]\[ h(t) = -16t^2 + 128t \][/tex]
where [tex]\( t \)[/tex] is the time in seconds.

### Part a: Time to reach maximum height

The height function is a parabola that opens downwards (since the coefficient of [tex]\( t^2 \)[/tex] is negative). The maximum height is at the vertex. The time [tex]\( t \)[/tex] at which the maximum height occurs is given by the formula for the vertex of a quadratic equation:

[tex]\[ t = -\frac{b}{2a} \][/tex]

Here, the coefficients are [tex]\( a = -16 \)[/tex] and [tex]\( b = 128 \)[/tex]. Plugging in these values:

[tex]\[ t = -\frac{128}{2 \times (-16)} = 4 \][/tex]

So, it takes 4 seconds for the rocket to reach its maximum height.

### Part b: Maximum height

To find the maximum height, substitute [tex]\( t = 4 \)[/tex] back into the height equation:

[tex]\[ h(4) = -16(4)^2 + 128(4) \][/tex]

Calculate each term:
- [tex]\( 4^2 = 16 \)[/tex]
- [tex]\( -16 \times 16 = -256 \)[/tex]
- [tex]\( 128 \times 4 = 512 \)[/tex]

Add them together:
[tex]\[ h(4) = -256 + 512 = 256 \][/tex]

Thus, the maximum height is 256 feet.

### Part c: Time to reach the ground

The rocket reaches the ground when its height [tex]\( h(t) \)[/tex] is 0. We solve the equation:

[tex]\[ -16t^2 + 128t = 0 \][/tex]

Factor out [tex]\( t \)[/tex]:
[tex]\[ t(-16t + 128) = 0 \][/tex]

This gives two solutions:
1. [tex]\( t = 0 \)[/tex]: The time at launch.
2. [tex]\( -16t + 128 = 0 \)[/tex]: Solve for [tex]\( t \)[/tex].

[tex]\[ -16t = -128 \][/tex]
[tex]\[ t = \frac{128}{16} = 8 \][/tex]

So, it takes 8 seconds for the rocket to reach the ground.

In summary:
- The rocket reaches its maximum height at 4 seconds.
- The maximum height is 256 feet.
- The rocket takes 8 seconds to come back to the ground.

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