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The blades of a windmill turn on an axis that is 40 feet from the ground. The blades are 15 feet long and complete 3 rotations every minute. Write a sine model, [tex]y = a \sin(b t) + k[/tex], for the height (in feet) of the end of one blade as a function of time [tex]t[/tex] (in seconds). Assume the blade is pointing to the right when [tex]t=0[/tex] and that the windmill turns counterclockwise at a constant rate.

- [tex]a[/tex] is the amplitude, which is the length of the blade: [tex]a = 15[/tex].
- The vertical shift, [tex]k[/tex], is the height of the windmill's axis: [tex]k = 40[/tex].

To find the period and [tex]b[/tex]:
- The windmill completes 3 rotations per minute, which means the period is [tex]\frac{60}{3} = 20[/tex] seconds.
- The formula for the period of a sine function is [tex]\frac{2\pi}{b}[/tex]. Therefore, [tex]b = \frac{2\pi}{20} = \frac{\pi}{10}[/tex].

Thus, the sine model is:

[tex]y = 15 \sin\left(\frac{\pi}{10} t\right) + 40[/tex].

Answer :

To solve the problem of writing a sine model for the height of the end of a windmill blade as a function of time, let's break it down step-by-step:

1. Determine the Amplitude (a):
- The amplitude represents the length of the blades. Since the blades are 15 feet long, the amplitude [tex]\(a\)[/tex] is 15.

2. Identify the Vertical Shift (k):
- The blades of the windmill rotate around an axis that is 40 feet above the ground. This height is the vertical shift, [tex]\(k\)[/tex], so [tex]\(k = 40\)[/tex].

3. Calculate the Period:
- The windmill completes 3 rotations every minute, meaning in one minute (60 seconds), the windmill makes 3 full rotations.
- To find the period (the time it takes for one full rotation), divide 60 seconds by the number of rotations per minute: [tex]\(\text{Period} = \frac{60 \text{ seconds}}{3}\)[/tex], which gives a period of 20 seconds.

4. Determine the Value of [tex]\(b\)[/tex]:
- The sine function's period is related to the coefficient [tex]\(b\)[/tex] by the formula: [tex]\(\text{Period} = \frac{2\pi}{b}\)[/tex].
- Since we have computed the period as 20 seconds, we can find [tex]\(b\)[/tex] using the relation: [tex]\(b = \frac{2\pi}{20}\)[/tex].
- Solving for [tex]\(b\)[/tex] gives approximately [tex]\(b = 0.314\)[/tex].

5. Write the Sine Model:
- The function for the height [tex]\(y\)[/tex] of the end of one blade at time [tex]\(t\)[/tex] in seconds is given by:
[tex]\[
y = a \sin(bt) + k
\][/tex]
- Substituting in the values we found:
[tex]\[
y = 15 \sin(0.314 t) + 40
\][/tex]

This equation models the height of the end of a windmill blade in terms of time [tex]\(t\)[/tex], where [tex]\(t\)[/tex] is measured in seconds.

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Rewritten by : Barada