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1.8. Worked Examples
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Let's begin by discussing the average rate of change. Can anyone tell me what it means?
Isn't it how much something changes on average over a specific interval?
"Exactly! We calculate this using the formula:
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Now, let’s shift gears to the instantaneous rate of change, or IROC. What do you think this means?
Isn’t it just how fast something is changing at a specific moment?
Spot on! This is calculated using the derivative of the function. For example, for , the derivative is:
"
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Create a free accountNow that we’ve discussed both AROC and IROC, let’s see how they might apply together.
Can you give an example where we would use both?
Certainly! Consider a ball thrown into the air. We can find the average rate of change of its height over a time interval, say from 1 to 3 seconds, and determine how high it is rising on average.
And then we could find the instantaneous rate at the peak, right?
Exactly! We find the instantaneous rate of change when the ball reaches its maximum height to understand that moment of stillness.
Let’s summarize: AROC gives us overall change in an interval, while IROC provides specific change at a point. Both are key to understanding motion!
Overview
Short Summary
This section presents worked examples that illustrate average and instantaneous rates of change.
Medium Summary
In this section, we explore worked examples that demonstrate both the average rate of change and instantaneous rate of change in various contexts, helping to clarify these key concepts in calculus.
Detailed Summary
Worked Examples
In this section, we delve into practical applications of the concepts of average and instantaneous rates of change. We present worked examples that illustrate how to calculate these rates using specific functions. First, we’ll examine the average rate of change, which provides insight into overall trends within a defined interval. Then, we'll explore instantaneous rates of change, focusing on how to determine the derivative at a specific point for a function. Understanding these examples is essential for applying calculus concepts to real-world scenarios, such as motion and growth phenomena.
Audio Book
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Create a free account🔍 Example 1: A ball is thrown into the air. Its height in meters after 𝑡 seconds is given by: ℎ(𝑡) = −5𝑡² + 20𝑡 + 2
a) Find the average rate of change of height from 𝑡 = 1 to 𝑡 = 3:
h(3) = -5(3)² + 20(3) + 2 = -45 + 60 + 2 = 17 \ ext{AROC} = \frac{17 - 17}{3 - 1} = 0$$ Interpretation: The average change in height over this interval is 0; the ball returned to the same height.Detailed Explanation
In this example, we are tasked with finding the average rate of change (AROC) of the height of a ball thrown into the air over a specified time interval from 1 to 3 seconds. We first calculate the height at both 𝑡 = 1 and 𝑡 = 3 using the function ℎ(𝑡) = −5𝑡² + 20𝑡 + 2.
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Calculate each height:
- For 𝑡 = 1, substitute into the equation:
- ℎ(1) = −5(1)² + 20(1) + 2 → ℎ(1) = 17
- For 𝑡 = 3, do the same:
- ℎ(3) = −5(3)² + 20(3) + 2 → ℎ(3) = 17
- For 𝑡 = 1, substitute into the equation:
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Calculate the AROC:
- Use the formula for AROC = (f(b) - f(a)) / (b - a)
- AROC = (17 - 17) / (3 - 1) = 0
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Interpretation: This means that between 1 and 3 seconds, the average height does not change, indicating that the ball reached its peak height and then returned to that same height.
Examples & Analogies
Think of the height of a person riding a Ferris wheel. If they reach the top at 1 second and then come back down to the same height at 3 seconds, their average height hasn't changed during that time. Even though they might have been moving up and down, the average height when looking only at those two points is the same.
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Create a free accountb) Find the instantaneous rate of change at 𝑡 = 2:
h'(2) = -10(2) + 20 = 0$$ Interpretation: The ball is at its peak at 𝑡 = 2 (momentarily not moving up or down).Detailed Explanation
Next, we find the instantaneous rate of change (IROC) of the height at the exact moment when the ball has been in the air for 2 seconds. To do this, we need to find the derivative of the height function ℎ(𝑡) with respect to time:
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Differentiation:
- Differentiate ℎ(𝑡) = −5𝑡² + 20𝑡 + 2:
- h'(t) = -10t + 20
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Calculate the IROC at 𝑡 = 2:
- Substitute 2 into the derivative:
- h'(2) = -10(2) + 20 = 0
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Interpretation: This tells us that at 𝑡 = 2 seconds, the height is not changing anymore, which means the ball has reached its peak. At that moment, its speed is exactly zero; it is neither going up nor down.
Examples & Analogies
Consider the moment when a basketball reaches the top of its arc right before starting to come down. Just like the ball's height wouldn't change at the peak (zero speed moment), the ball being thrown also has a moment at the peak of its flight where it briefly stops rising before descending.
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Key Concepts
Core takeaways and short definitions to help you quickly recall the key ideas from this section.
Average Rate of Change: This is a measure of how much a quantity changes on average over a specified interval.
Instantaneous Rate of Change: This defines how quickly a function is changing at a specific instant and is represented by the derivative.
Derivative: The mathematical representation of the instantaneous rate of change of a function.
Secant Line: A line linking two points on a curve, representing the average rate of change.
Tangent Line: A line that touches a curve at a single point, indicating the instantaneous rate of change.
Examples
Memory Aids
Interactive tools to help you remember key concepts
Flash Cards
Glossary
Average Rate of Change
The ratio of the change in the value of a function over a specific interval to the change in the variable.
Instantaneous Rate of Change
The rate at which a function is changing at a specific point, determined by the derivative.
Derivative
A function that describes the instantaneous rate of change of another function.
Secant Line
A line that connects two points on a curve.
Tangent Line
A line that touches a curve at a single point, representing the instantaneous rate of change at that point.