Chapter 27: Problem 57
Solve the given problems. When air friction is considered, the time \(t\) (in \(\mathrm{s}\) ) it takes a certain falling object to attain a velocity \(v\) (in \(\mathrm{ft} / \mathrm{s}\) ) is given by \(t=5 \ln \frac{16}{16-0.1 v} .\) Find \(d t / d v\) for \(v=100 \mathrm{ft} / \mathrm{s}\)
Short Answer
Expert verified
The derivative \( \frac{dt}{dv} \) at \( v = 100 \) is \( \frac{2}{9} \).
Step by step solution
01
Understand the function
We start with the function given by the exercise: \( t = 5 \ln \frac{16}{16-0.1v} \). We need to find the derivative, \( \frac{dt}{dv} \), when \( v = 100 \, \text{ft/s} \).
02
Apply the chain rule
We need to apply the chain rule to differentiate \( t = 5 \ln \left( \frac{16}{16-0.1v} \right) \). Let \( u = \frac{16}{16-0.1v} \). Then, \( t = 5 \ln(u) \).
03
Differentiate the outer function
Differentiate \( t = 5 \ln(u) \) with respect to \( u \). The derivative is \( \frac{dt}{du} = \frac{5}{u} \).
04
Differentiate the inner function
Differentiate \( u = \frac{16}{16-0.1v} \) with respect to \( v \). Using the chain rule and recognizing it as a quotient, \( u = 16(16-0.1v)^{-1} \), we find \( \frac{du}{dv} = \frac{1.6}{(16-0.1v)^2} \).
05
Combine derivatives to find \( \frac{dt}{dv} \)
Combine the derivatives using the chain rule: \( \frac{dt}{dv} = \frac{dt}{du} \cdot \frac{du}{dv} = \frac{5}{u} \cdot \frac{1.6}{(16-0.1v)^2} = \frac{1.6 \times 5}{(16-0.1v) \cdot (16-0.1v)} \). Substitute back \( u = \frac{16}{16-0.1v} \).
06
Evaluate at \( v = 100 \)
Substitute \( v = 100 \) into \( \frac{dt}{dv} = \frac{8}{(16-0.1v)^2} \). Simplify to \( \frac{8}{(16-10)^2} = \frac{8}{36} = \frac{2}{9} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Derivative
The derivative is a fundamental concept in calculus. It represents how a function changes as its input changes. In mathematical terms, a derivative tells us "the rate of change" or "the slope" at any point of a function. In the context of our problem, we are looking at how time changes with respect to velocity.
- The function given is \( t = 5 \ln \left( \frac{16}{16-0.1v} \right) \).
- Our aim is to find \( \frac{dt}{dv} \), which is the rate at which time \( t \) changes when velocity \( v \) changes.
Chain Rule
The chain rule is a technique in differentiation used whenever we want to differentiate a function composed of other functions, especially when functions are "chained" together.In our example, the function \( t = 5 \ln \left( \frac{16}{16-0.1v} \right) \) is composed of two functions: the logarithm and the quotient inside it. We identify:
- The "outer function" is \( 5 \ln(u) \).
- The "inner function" is \( u = \frac{16}{16-0.1v} \).
Differentiation
Differentiation is the process of finding a derivative. It's a powerful tool in calculus that enables us to understand how quantities change relative to each other. In our task, differentiation helps us find \( \frac{dt}{dv} \), the derivative of time \( t \) with respect to velocity \( v \).Key steps in differentiation include:
- Identifying all components of the functions involved.
- Applying appropriate rules, such as the chain rule here.
- Simplifying the outcome to arrive at a clean expression.
Velocity-Time Relationship
In calculus, understanding the velocity-time relationship is crucial to solving real-world physics problems. This relationship reveals how a change in an object's velocity impacts the time it takes to reach that velocity. Our exercise focuses on understanding this relationship considering air friction.
- The function \( t = 5 \ln \left( \frac{16}{16-0.1v} \right) \) represents how long it takes an object to reach a velocity \( v \) with air resistance considered.
- By finding \( \frac{dt}{dv} \), we explore how small changes in velocity (\( v \)) affect the time (\( t \)) it takes to reach that velocity.