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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.

1. The amplitude, [tex]a[/tex], is the length of the blade:
[tex]a = 15[/tex]

2. The vertical shift, [tex]k[/tex], is the height of the axis from the ground:
[tex]k = 40[/tex]

3. The period is calculated using the rotations per minute:
The windmill completes 3 rotations per minute, which is 1 rotation every 20 seconds.
The period is [tex]20[/tex] seconds.

4. The frequency [tex]b[/tex] is given by:
[tex]b = \frac{2\pi}{\text{period}} = \frac{2\pi}{20} = \frac{\pi}{10}[/tex]

Now, the complete sine model for the height is:
[tex]y = 15 \sin\left(\frac{\pi}{10} t\right) + 40[/tex]

Answer :

To solve the problem of modeling the height of the end of a windmill blade as a sine function, we need to follow certain steps based on the data provided.

1. Understand the Components of the Sine Model:
The general sine model given is [tex]\( y = a \sin(b t) + k \)[/tex], where:
- [tex]\( a \)[/tex] is the amplitude of the sine wave.
- [tex]\( b \)[/tex] is related to the period of the sine wave.
- [tex]\( k \)[/tex] is the vertical shift of the sine wave.

2. Identify the Amplitude [tex]\( a \)[/tex]:
The amplitude [tex]\( a \)[/tex] is the maximum deviation of the wave from its central position, which in this case is equal to the length of the windmill blades.
Therefore, [tex]\( a = 15 \)[/tex] feet.

3. Determine the Vertical Shift [tex]\( k \)[/tex]:
The vertical shift [tex]\( k \)[/tex] is the height of the axis from the ground, which means it shifts the sine wave vertically.
Here, [tex]\( k = 40 \)[/tex] feet.

4. Calculate the Period of the Sine Wave:
Since the windmill completes 3 rotations every minute, it makes 1 rotation in [tex]\( \frac{60}{3} = 20 \)[/tex] seconds.
Hence, the period of one complete rotation, [tex]\( T \)[/tex], is 20 seconds.

5. Calculate [tex]\( b \)[/tex] from the Period:
The relationship between [tex]\( b \)[/tex] and the period is given by the formula [tex]\( T = \frac{2\pi}{b} \)[/tex].
Solving for [tex]\( b \)[/tex], we get [tex]\( b = \frac{2\pi}{T} \)[/tex].
Substituting the period, [tex]\( b = \frac{2\pi}{20} = 0.3141592653589793 \)[/tex].

By gathering all this information, the completed sine model for the height [tex]\( y \)[/tex] of the windmill blade is:

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

In this model:
- [tex]\( a = 15 \)[/tex] represents the blade length.
- The vertical shift [tex]\( k = 40 \)[/tex] is the height of the axis above the ground.
- The period is 20 seconds, with [tex]\( b = 0.3141592653589793 \)[/tex].

This function models the height of the tip of a windmill blade over time as it rotates.