Chapter 2: Problem 20
Ssuppose that a particle following the given path \(\mathbf{c}(t)\) flies off on a tangent at \(t=t_{0} .\) Compute the position of the particle at the given time \(t_{1}.\) $$\mathbf{c}(t)=\left(e^{t}, e^{-t}, \cos t\right), \text { where } t_{0}=1, t_{1}=2$$
Short Answer
Expert verified
The position of the particle at \(t=2\) is approximately \((5.436, 0, -0.301)\).
Step by step solution
01
Differentiate the position vector
To find the direction of the tangent vector at time \(t_0\), we start by differentiating \(\mathbf{c}(t) = (e^t, e^{-t}, \cos t)\) with respect to \(t\). The derivative is \(\mathbf{c}'(t) = (e^t, -e^{-t}, -\sin t)\).
02
Evaluate the tangent vector at \(t_0\)
Substitute \(t_0 = 1\) into the derivative to get the tangent vector at \(t_0\). That is \(\mathbf{c}'(1) = (e^1, -e^{-1}, -\sin 1)\). Calculate the numerical values: \(\mathbf{c}'(1) \approx (2.718, -0.368, -0.841)\).
03
Find the position at \(t_0\)
Substitute \(t_0 = 1\) into the position function \(\mathbf{c}(t)\) to get the position vector at \(t_0\). Thus, \(\mathbf{c}(1) = (e^1, e^{-1}, \cos 1)\) which approximately equals \((2.718, 0.368, 0.54)\).
04
Compute the line equation from \(t_0\)
The line of motion has the form \(\mathbf{r}(t) = \mathbf{c}(t_0) + (t - t_0) \mathbf{c}'(t_0)\). Substitute our known values, \(\mathbf{r}(t) = (2.718, 0.368, 0.54) + (t-1)(2.718, -0.368, -0.841)\).
05
Evaluate the line equation at \(t_1\)
Substitute \(t_1 = 2\) into the line equation from Step 4.\(\mathbf{r}(2) =(2.718, 0.368, 0.54) + (2-1)(2.718, -0.368, -0.841) = (2.718 + 2.718, 0.368 - 0.368, 0.54 - 0.841)\).
06
Simplify to find the position
Simplify the expression: \(\mathbf{r}(2) = (5.436, 0, -0.301)\). This represents the position of the particle at \(t = 2\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Differentiation
Differentiation is a fundamental concept in calculus used to determine the rate at which a function is changing at any point. It serves as a powerful tool to find the slope or gradient of a curve described by a function. For a particle moving along a path defined by a position vector, differentiation is required to compute what is known as the tangent vector.
- Differentiating the position vector gives you the rate of change in position, which is effectively the velocity of the particle.
- This derivative is particularly important in understanding how the trajectory of the particle changes over time, allowing us to study its motion intricately.
- In this exercise, we're differentiating the position vector \((e^t, e^{-t}, \cos t)\) to find the vector's derivative \((e^t, -e^{-t}, -\sin t)\).
Particle Path
The path of a particle is defined by its position vector, which indicates its location in a space x-y-z coordinate system at any point in time. This path is the trajectory that a particle follows as a function of time and can be expressed as a vector function like \((e^t, e^{-t}, \cos t)\).
- This vector function is composed of three individual functions corresponding to the x, y, and z axes.
- Each component describes how position on each axis changes with respect to time \(t\).
Position Vector
The position vector is a key concept in vector calculus and physics. It specifies the exact position of a particle in space at a particular time. In this context, the position vector is noted as \(\mathbf{c}(t) = (e^t, e^{-t}, \cos t)\).
- The position vector combines all three dimensions - x, y, and z - into a single vector function.
- It is a function of time, meaning as time progresses, the position of the particle in space also changes.
Tangent Vector
The tangent vector represents the direction and speed of motion of a particle at any given instant along its path. In other words, it is the velocity vector obtained from differentiating the position vector.
- At a given time \(t_0\), the tangent vector helps determine how the particle will move if it continues in a straight line from that point.
- In our exercise, the tangent vector at \(t_0 =1\) is calculated as \((e^1, -e^{-1}, -\sin 1)\) which numerically evaluates to approximately \(2.718, -0.368, -0.841\).
Line Equation
The line equation is derived to determine the future position of a particle, assuming it continues its path along the tangent vector from a given starting position. The line equation takes the form:
- \(\mathbf{r}(t) = \mathbf{c}(t_0) + (t - t_0) \cdot \mathbf{c}'(t_0)\)
- It originates at the particle's current position and is directed along the tangent vector, allowing us to track its subsequent motion.