Math Problem Statement

Suppose you are 15 meters high on a Ferris wheel whose diameter is 20 meters, that the wheel makes one full rotation every 3 minutes, and that you boarded at ground level (the 6:00 position). How long might you have been on the wheel? Is this is the only possibility? Provide one answer between 0 and 3 minutes. You could've been on the ferris wheel for minutes.

Solution

We need to model your position on the Ferris wheel, which involves periodic motion. Here's the breakdown:

Key Information:

  • The diameter of the Ferris wheel is 20 meters, so the radius is half of that:
    r=10r = 10 meters.
  • You are 15 meters high, meaning you are 15 meters above the ground.
  • The Ferris wheel completes one full rotation every 3 minutes.
  • You boarded at the 6:00 position, which is on the ground.

Step 1: Modeling the Motion

Since the Ferris wheel makes a full rotation every 3 minutes, we can model the height h(t)h(t) of your position as a function of time using the sine function. The general form of the vertical position on a Ferris wheel is:

h(t)=rsin(ωt+ϕ)+Ch(t) = r \cdot \sin(\omega t + \phi) + C

where:

  • r=10r = 10 meters (radius),
  • ω=2π3\omega = \frac{2\pi}{3} radians per minute (angular velocity, since it takes 3 minutes for one full rotation),
  • C=10C = 10 meters (the center of the wheel is 10 meters above the ground),
  • ϕ\phi is the phase shift, which we will determine,
  • h(t)h(t) is the height at time tt.

Step 2: Find the Height Function

At t=0t = 0 (the moment you board), your height is at ground level, so:

h(0)=10sin(0+ϕ)+10=0h(0) = 10 \cdot \sin(0 + \phi) + 10 = 0

Solving for ϕ\phi, we get:

sin(ϕ)=1ϕ=π2\sin(\phi) = -1 \quad \Rightarrow \phi = -\frac{\pi}{2}

Thus, the height function becomes:

h(t)=10sin(2π3tπ2)+10h(t) = 10 \cdot \sin\left( \frac{2\pi}{3} t - \frac{\pi}{2} \right) + 10

Step 3: Solve for Time

You are 15 meters high at some point on the Ferris wheel. Therefore, we set h(t)=15h(t) = 15:

15=10sin(2π3tπ2)+1015 = 10 \cdot \sin\left( \frac{2\pi}{3} t - \frac{\pi}{2} \right) + 10

Simplifying:

5=10sin(2π3tπ2)5 = 10 \cdot \sin\left( \frac{2\pi}{3} t - \frac{\pi}{2} \right)

12=sin(2π3tπ2)\frac{1}{2} = \sin\left( \frac{2\pi}{3} t - \frac{\pi}{2} \right)

The sine of 12\frac{1}{2} occurs at π6\frac{\pi}{6} and 5π6\frac{5\pi}{6}. Thus, we have two possible solutions for 2π3tπ2\frac{2\pi}{3} t - \frac{\pi}{2}:

  1. 2π3tπ2=π6\frac{2\pi}{3} t - \frac{\pi}{2} = \frac{\pi}{6}
  2. 2π3tπ2=5π6\frac{2\pi}{3} t - \frac{\pi}{2} = \frac{5\pi}{6}

Step 4: Solve for tt

Case 1: 2π3tπ2=π6\frac{2\pi}{3} t - \frac{\pi}{2} = \frac{\pi}{6}

2π3t=π6+π2=2π3\frac{2\pi}{3} t = \frac{\pi}{6} + \frac{\pi}{2} = \frac{2\pi}{3}

t=2π3×32π=1 minutet = \frac{2\pi}{3} \times \frac{3}{2\pi} = 1 \text{ minute}

Case 2: 2π3tπ2=5π6\frac{2\pi}{3} t - \frac{\pi}{2} = \frac{5\pi}{6}

2π3t=5π6+π2=8π6=4π3\frac{2\pi}{3} t = \frac{5\pi}{6} + \frac{\pi}{2} = \frac{8\pi}{6} = \frac{4\pi}{3}

t=4π3×32π=2 minutest = \frac{4\pi}{3} \times \frac{3}{2\pi} = 2 \text{ minutes}

Step 5: Conclusion

You could have been on the Ferris wheel for either 1 minute or 2 minutes. Both are valid solutions for the given height of 15 meters.

Would you like more details or have any further questions about the solution?

Additional Questions:

  1. How would the position of a person on the Ferris wheel change if the wheel rotated faster or slower?
  2. What would the height function look like if you started at the highest point (12:00 position)?
  3. How do the phase shifts in the equation relate to the starting position of the person on the Ferris wheel?
  4. What other heights can you calculate for specific times during the rotation?
  5. How could this problem change if the Ferris wheel were not perfectly circular?

Tip:

In problems involving periodic motion, using sine or cosine functions helps model the motion based on known characteristics like amplitude (radius) and frequency (how fast the rotation is).

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Periodic Functions
Harmonic Motion

Formulas

h(t) = r * sin(ωt + φ) + C
ω = 2π / T
sin(θ) = opposite / hypotenuse

Theorems

Sine Function in Circular Motion
Phase Shift in Trigonometric Functions

Suitable Grade Level

Grades 10-12