Chapter 12: Problem 26
Find the curvature \(K\) of the plane curve at the given value of the parameter. \(\mathbf{r}(t)=t^{2} \mathbf{j}+\mathbf{k}, \quad t=0\)
Short Answer
Expert verified
The curvature of the plane curve at \(t=0\) is undefined
Step by step solution
01
Calculate the derivative of the vector function
The vector function \(\mathbf{r}(t)=t^{2} \mathbf{j}+\mathbf{k}\). Differentiating \(\mathbf{r}(t)\) with respect to \(t\), we get \[\mathbf{v}(t)= \mathbf{r}'(t) = 2t \mathbf{j}\].
02
Calculate the velocity and acceleration at t=0
Evaluating this at \(t=0\), we find \(\mathbf{v}(0) = \mathbf{0}\). Now, calculate the second derivative of \( \mathbf{r}(t) \), i.e., take the derivative of \( \mathbf{v}(t) \). We obtain \[\mathbf{a}(t) = \mathbf{v}'(t) = 2 \mathbf{j}\].At \(t=0\), this gives \(\mathbf{a}(0) = 2\mathbf{j}\).
03
Compute the curvature
Substitute the obtained values into the formula of curvature \(K = |\mathbf{v} \times \mathbf{a}| / |\mathbf{v}|^3 \). Since \(\mathbf{v}(0) = \mathbf{0}\), the magnitude of the cross product \(|\mathbf{v} \times \mathbf{a}|\) equals 0. Therefore, the curvature at \(t=0\) is \(K = 0 / 0\), which is undefined.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Plane Curve
When dealing with a plane curve, imagine a smooth path on a two-dimensional surface. Just like drawing a line on paper. These curves can be represented mathematically using vector functions, providing a way to study properties like direction, length, and shape. In our given exercise, we have a plane curve defined by the vector function \( \mathbf{r}(t) = t^{2} \mathbf{j} + \mathbf{k} \). Here, the curve lies in the \( j-k \) plane. Break it down and you'll see:
- \( t^2 \mathbf{j} \) means as \( t \) changes, the curve moves through points on the \( j \)-axis.
- \( \mathbf{k} \) signifies movement along the \( k \)-axis.
Vector Function
A vector function is a function that outputs a vector for every input value. Think of vector functions as providing a map with directions in space. In calculus, it is a powerful tool that represents a path or curve in a multi-dimensional space. For our exercise, the vector function is given by \( \mathbf{r}(t) = t^{2} \mathbf{j} + \mathbf{k} \). This means:
- Each value of \( t \) gives a corresponding point on the plane, characterized by the combination \( (t^2, 1) \) in the \( j-k \) plane.
- The function outputs a position vector \( (0, t^2, 1) \) in three-dimensional space.
Calculus Problem-Solving
Solving calculus problems involves a systematic approach. It often requires understanding derivatives, rates of change, and geometric properties of functions. In the context of the original exercise:
- We need to find how curves bend or twist, known as curvature, at a specific parameter \( t=0 \).
- The process involves differentiating vector functions to calculate velocity and acceleration vectors.
- For curvature \( K \), use the formula \( K = |\mathbf{v} \times \mathbf{a}| / |\mathbf{v}|^3 \).
Derivatives in Calculus
Derivatives are foundational elements in calculus, providing a method to understand how functions change. In the context of vector functions, derivatives help identify rates of movement and change direction. For instance, in the original exercise:
- The first derivative \( \mathbf{v}(t) = \mathbf{r}'(t) = 2t \mathbf{j} \) represents the velocity.
- The second derivative \( \mathbf{a}(t) = \mathbf{v}'(t) = 2\mathbf{j} \) indicates the acceleration.