Ferris Wheel Trig Problem

Khan Academy
8 Dec 200707:21
EducationalLearning
32 Likes 10 Comments

TLDRThe video script details a mathematical problem involving Jacob and Emily riding a 16-meter diameter Ferris wheel in Billings, Montana. The wheel turns at a rate of 3 revolutions per minute, and the height of the riders above the ground is modeled as a sinusoidal function of time, with the lowest point at 1 meter above ground level. The script explains how to derive the equation for their height 'h' as a function of time 't' in seconds, considering the wheel's rotation speed and the geometry of the situation. The final equation is h = 9 - 8cos(18t), which represents the height in meters as a function of time in seconds, and the script promises to graph this function in a subsequent video.

Takeaways
  • πŸŽͺ Jacob and Emily are riding a Ferris wheel at a carnival in Billings, Montana.
  • πŸ”΅ The Ferris wheel has a diameter of 16 meters, which means its radius is 8 meters.
  • πŸ“ The lowest point of the Ferris wheel is 1 meter above the ground.
  • ⏱ The Ferris wheel completes 3 revolutions per minute, equating to 18 degrees per second.
  • πŸ“‰ The height h of Jacob and Emily above the ground is described as a sinusoidal function of time.
  • ⏳ At t = 0, they are at the lowest point of the Ferris wheel.
  • πŸ“ The problem involves calculating the height h as a function of time t in seconds.
  • πŸ“ˆ The Ferris wheel's rotation speed is converted into degrees per second to relate it to the sinusoidal function.
  • πŸ“Š The height h is determined using trigonometric relationships, specifically cosine, in relation to the angle of rotation.
  • 🧩 The final equation for h as a function of t is h = 9 - 8cos(18t).
  • πŸ“Š The next step is to graph the function h = 9 - 8cos(18t) to visualize the sinusoidal motion.
Q & A
  • What is the diameter of the Ferris wheel that Jacob and Emily are riding?

    -The diameter of the Ferris wheel is 16 meters.

  • What is the radius of the Ferris wheel?

    -The radius of the Ferris wheel is half of its diameter, which is 8 meters.

  • At what height is the lowest point of the Ferris wheel above the ground?

    -The lowest point of the Ferris wheel is 1 meter above the ground.

  • How many revolutions per minute does the Ferris wheel make?

    -The Ferris wheel makes 3 revolutions per minute.

  • What is the relationship between the number of revolutions and the angle covered per second?

    -Since the Ferris wheel makes 3 revolutions per minute, it covers 360 degrees per 20 seconds, which simplifies to 18 degrees per second.

  • What is the sinusoidal function of time that represents Jacob and Emily's height above the ground?

    -The sinusoidal function representing their height h above the ground as a function of time t is h(t) = 9 - 8cos(18t).

  • Why is the cosine function used to relate the height to the angle?

    -The cosine function is used because it relates the adjacent side (9 - h) to the hypotenuse (8 meters) in a right-angled triangle, which is formed by the height, radius, and the angle of rotation.

  • What is the significance of the number 18 in the equation h(t) = 9 - 8cos(18t)?

    -The number 18 represents the rate of change in degrees per second, which is derived from the Ferris wheel's speed of 3 revolutions per minute.

  • What is the initial height of Jacob and Emily above the ground when t equals 0?

    -At t equals 0, which is the lowest point on the wheel, their height above the ground is 1 meter plus the radius of the Ferris wheel, which is 9 meters.

  • How does the height of Jacob and Emily change as they ride the Ferris wheel?

    -Their height changes sinusoidally with time, increasing and decreasing as they move around the Ferris wheel, following the equation h(t) = 9 - 8cos(18t).

  • What will be the next step after deriving the equation for h(t)?

    -The next step mentioned in the script is to graph the function h(t) to visualize how the height changes over time as Jacob and Emily ride the Ferris wheel.

Outlines
00:00
🎑 Jacob and Emily's Ferris Wheel Ride

The script describes a scenario where Jacob and Emily are riding a ferris wheel at a carnival in Billings, Montana. The wheel has a diameter of 16 meters, which means its radius is 8 meters. The lowest point of the wheel is 1 meter above the ground. The height of Jacob and Emily above the ground, denoted as 'h', is said to be a sinusoidal function of time 't', with 't=0' representing the lowest point on the wheel. The wheel turns at a rate of 3 revolutions per minute, which translates to 18 degrees per second. The script aims to derive an equation for 'h' as a function of 't', given in seconds.

05:01
πŸ“š Deriving the Height Function for the Ferris Wheel Ride

In this paragraph, the script explains the process of deriving the mathematical function for the height 'h' of Jacob and Emily on the ferris wheel as a function of time 't'. It starts by establishing that the wheel makes 3 revolutions per minute, which is equivalent to 18 degrees per second. The script then uses trigonometry to relate the angle of rotation to their height above the ground. By considering the right triangle formed by the radius of the wheel, the height above the ground, and the horizontal distance from the center to the edge of the wheel, the cosine function is used to express 'h'. The final equation derived is h = 9 - 8cos(18t), where 'h' is the height above the ground in meters, and 't' is the time in seconds. The script concludes with the intention to graph this function in the next video.

Mindmap
Keywords
πŸ’‘Ferris Wheel
A Ferris wheel is a large vertical or slanting axle with passenger cabins or seats arranged around the circumference, designed for amusement at fairs and carnivals. In the video's context, Jacob and Emily ride a Ferris wheel at a carnival in Billings, Montana, which serves as the central focus for the mathematical problem being discussed.
πŸ’‘Diameter
Diameter refers to the distance across the widest part of a circle or ellipse, passing through the center. In the video, the Ferris wheel has a diameter of 16 meters, which is used to calculate the radius and subsequently the height above the ground as the wheel turns.
πŸ’‘Radius
The radius is the distance from the center of a circle to any point on its circumference. In the script, the radius of the Ferris wheel is half of its diameter, which is 8 meters, and it plays a crucial role in determining the height of Jacob and Emily as they ride.
πŸ’‘Sinusoidal Function
A sinusoidal function is a mathematical function that describes a smooth, periodic oscillation. In the video, it is assumed that Jacob and Emily's height above the ground follows a sinusoidal pattern over time, which is a key concept in formulating the equation for their motion.
πŸ’‘Time (t)
In the context of the video, time (t) represents the variable used in the sinusoidal function to measure the position of Jacob and Emily on the Ferris wheel at any given moment. The script specifies that t equals 0 corresponds to the lowest point on the wheel.
πŸ’‘Revolutions Per Minute (RPM)
Revolutions per minute (RPM) is a measure of rotational speed, indicating how many complete rotations occur within a minute. The Ferris wheel in the script turns at 3 revolutions per minute, which is essential in calculating the angular velocity and the height function.
πŸ’‘Degrees
Degrees are a unit of measurement for angles, with a full circle encompassing 360 degrees. The script uses degrees to describe the angular movement of the Ferris wheel, with 360 degrees equating to one full revolution and 18 degrees per second being the rate of rotation.
πŸ’‘Trigonometric Functions
Trigonometric functions, such as sine and cosine, relate the angles of a triangle to the lengths of its sides. In the video, cosine is used to relate the height of Jacob and Emily to the angle formed as the Ferris wheel rotates, helping to derive the height function.
πŸ’‘Hypotenuse
The hypotenuse is the longest side of a right-angled triangle, opposite the right angle. In the script, the hypotenuse is used to describe the radius of the Ferris wheel (8 meters) in the context of a right triangle formed by the height, the radius, and the angle of rotation.
πŸ’‘Cosine
Cosine is a trigonometric function that gives the ratio of the length of the adjacent side to the hypotenuse in a right-angled triangle. In the video, the cosine function is applied to find the relationship between the angle of rotation (18t degrees) and the height of Jacob and Emily above the ground.
πŸ’‘Graph
Graphing is the process of visually plotting data points on a coordinate system to understand the relationship between variables. The script mentions that the next step will be to graph the function expressing height as a function of time, which will visually represent the sinusoidal motion of the Ferris wheel.
Highlights

Jacob and Emily ride a ferris wheel at a carnival in Billings, Montana.

The ferris wheel has a 16-meter diameter.

Radius of the ferris wheel is half the diameter, which is 8 meters.

The lowest point of the ferris wheel is 1 meter above the ground.

Jacob and Emily's height above the ground is a sinusoidal function of time.

The ferris wheel turns at 3 revolutions per minute.

One revolution is equivalent to 360 degrees.

The ferris wheel rotates at 18 degrees per second.

The total number of degrees traveled in t seconds is 18t degrees.

The height h at any point is 1 meter plus the radius, which is 9 meters.

The height h can be expressed as a function of the angle 18t degrees.

A triangle is formed with the radius as the hypotenuse, and 9 - h as the adjacent side.

The cosine function relates the adjacent side to the hypotenuse at angle 18t degrees.

The equation for h as a function of t is derived using cosine.

The final equation for h(t) is h = 9 - 8cos(18t).

The next video will involve graphing the function h(t).

Transcripts
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