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A Ferris wheel has a diameter of 120 m - Leaving Cert Mathematics - Question 8 - 2022

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A Ferris wheel has a diameter of 120 m. When it is turning, it completes exactly 10 full rotations in one hour. The diagram above shows the Ferris wheel before it st... show full transcript

Worked Solution & Example Answer:A Ferris wheel has a diameter of 120 m - Leaving Cert Mathematics - Question 8 - 2022

Step 1

Complete the table below. The value of h(1) is given.

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Answer

To calculate h(t) for t = 0 to 8:

  • For t = 0: h(0)=7260cos(0)=72601=12h(0) = 72 - 60 \, \text{cos}(0) = 72 - 60 \cdot 1 = 12. So, h(0) = 12.

  • For t = 1: h(1) is given as 42.

  • For t = 2: h(2)=7260cos(π3)=72600.5=42h(2) = 72 - 60 \, \text{cos}\left( \frac{\pi}{3} \right) = 72 - 60 \cdot 0.5 = 42.

  • For t = 3: h(3)=7260cos(π2)=72600=72h(3) = 72 - 60 \, \text{cos}\left( \frac{\pi}{2} \right) = 72 - 60 \cdot 0 = 72.

  • For t = 4: h(4)=7260cos(2π3)=7260(0.5)=102h(4) = 72 - 60 \, \text{cos}\left( \frac{2\pi}{3} \right) = 72 - 60 \cdot (-0.5) = 102.

  • For t = 5: h(5)=7260cos(5π6)=7260(3/2)110.4h(5) = 72 - 60 \, \text{cos}\left( \frac{5\pi}{6} \right) = 72 - 60 \cdot (-\sqrt{3}/2) \approx 110.4.

  • For t = 6: h(6)=7260cos(2π)=72601=12h(6) = 72 - 60 \, \text{cos}(2\pi) = 72 - 60 \cdot 1 = 12.

  • For t = 7: h(7)=7260cos(7π6)=7260(0.5)=102h(7) = 72 - 60 \, \text{cos}\left( \frac{7\pi}{6} \right) = 72 - 60 \cdot (-0.5) = 102.

  • For t = 8: h(8)=7260cos(4π3)=7260(0.5)=110.4h(8) = 72 - 60 \, \text{cos}\left( \frac{4\pi}{3} \right) = 72 - 60 \cdot (-0.5) = 110.4.

The completed table values are:

t | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | h(t) | 12 | 42 | 42 | 72 | 102 | 110.4 | 12 | 102 | 110.4 |

Step 2

Find the period and range of h(t).

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Answer

The function h(t) is a cosine function, which has a period calculated as:

extPeriod=2ππ6=12 minutes. ext{Period} = \frac{2\pi}{\frac{\pi}{6}} = 12 \text{ minutes}.

The range values based on the minimum and maximum heights are:

  • Minimum height: 12 m
  • Maximum height: 132 m

Therefore, the range is:

Range=[12,132].\text{Range} = [12, 132].

Step 3

During a 50-minute period, what is the greatest number of minutes for which the point A could be higher than 42 m?

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Answer

To find how long point A is above 42 m, we can determine that:

  • From the table, point A is above 42 m in the intervals:
    • t = 0 to 4
    • t = 5 to 8

This gives us:

  • For 50 minutes: 50 minutes=4 minutes+2 periods=32 minutes50\text{ minutes} = 4\text{ minutes} + 2\text{ periods} \cdots = 32\text{ minutes}. Thus, the greatest number of minutes is 32.

Step 4

By solving the following equation, find the second time (value of t) that the point A is at a height of 110 m, after it starts turning.

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Answer

To solve the equation: 7260cos(π6t)=11072 - 60 \, \text{cos}\left( \frac{\pi}{6} t \right) = 110

Rearranging gives: 60cos(π6t)=38cos(π6t)=1930.60\text{cos}\left( \frac{\pi}{6} t \right) = -38 \quad \Rightarrow \quad \text{cos}\left( \frac{\pi}{6} t \right) = -\frac{19}{30}.

Using the cosine function: t = \frac{6}{\pi} \text{cos}^{-1}\left(-\frac{19}{30}\right)\approx 1.3\text{ and}: 3.8\text{ minutes}.

So, the second time is: ( t \approx 3.85 \text{ minutes}. )

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