High School

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]k[/tex] is the vertical shift, which is the height of the axis above the ground.
- Determine [tex]b[/tex] based on the number of rotations per minute.

Now, solve for:

- [tex]a = \text{length of the blade} = 15 \text{ feet}[/tex]
- [tex]k = \text{height of the axis} = 40 \text{ feet}[/tex]

Determine [tex]b[/tex] by considering the frequency of rotations. The windmill completes 3 rotations per minute, which is [tex]\frac{3}{60}[/tex] rotations per second.

Thus, the model becomes:

[tex]y = 15 \sin \left(\frac{6 \pi}{60} t \right) + 40[/tex] or simplified, [tex]y = 15 \sin \left(\frac{\pi}{10} t\right) + 40[/tex].

Answer :

To create a sine model for the height of the end of one blade of the windmill as a function of time [tex]\( t \)[/tex] (in seconds), let's break down the problem and find the components of the sine equation: [tex]\( y = a \sin(b t) + k \)[/tex].

1. Amplitude ([tex]\( a \)[/tex]):
- The amplitude is the maximum vertical distance the end of the blade moves from its central position.
- This distance is equal to the length of the blade, which is 15 feet.
- Therefore, [tex]\( a = 15 \)[/tex].

2. Angular Frequency ([tex]\( b \)[/tex]):
- The blades complete 3 rotations every minute. To find the frequency in terms of seconds, we first convert the rotations per minute to rotations per second:
- [tex]\( \text{Rotations per second} = \frac{3 \text{ rotations/minute}}{60 \text{ seconds/minute}} = 0.05 \text{ rotations/second} \)[/tex].
- The angular frequency [tex]\( b \)[/tex], which is in radians per second, is given by the formula [tex]\( b = 2\pi \times \text{frequency} \)[/tex].
- Therefore, [tex]\( b = 2\pi \times 0.05 = 0.3141592653589793 \)[/tex].

3. Vertical Shift ([tex]\( k \)[/tex]):
- The vertical shift corresponds to the height of the axis above the ground, which in this case is 40 feet.
- Thus, [tex]\( k = 40 \)[/tex].

Combining these components, the sine model for the height [tex]\( y \)[/tex] of the end of one blade as a function of time [tex]\( t \)[/tex] in seconds is:

[tex]\[ y = 15 \sin(0.3141592653589793 \times t) + 40 \][/tex]

This equation provides the height from the ground of the point at the tip of the blade over time, assuming the blade is pointing to the right when [tex]\( t=0 \)[/tex] and rotates counterclockwise.