Chapter 12: Problem 2
Evaluate the integrals. $$\int_{1}^{2}\left[(6-6 t) \mathbf{i}+3 \sqrt{t} \mathbf{j}+\left(\frac{4}{t^{2}}\right) \mathbf{k}\right] d t$$
Short Answer
Expert verified
The integral evaluates to \(-3 \mathbf{i} + (4\sqrt{2} - 2) \mathbf{j} + 2 \mathbf{k}\).
Step by step solution
01
Understanding the Integral
The given integral is a vector integral where each component of the vector function is integrated separately with respect to the variable \( t \). Since it is in the form \( \int_{1}^{2} \left[ f(t) \mathbf{i} + g(t) \mathbf{j} + h(t) \mathbf{k} \right] dt \), we will evaluate \( \int_{1}^{2} f(t) dt \), \( \int_{1}^{2} g(t) dt \), and \( \int_{1}^{2} h(t) dt \) to find each component separately.
02
Compute the Integral for \( \mathbf{i} \)-Component
The \( \mathbf{i} \)-component of the integrand is \( 6 - 6t \). We need to find:\[\int_{1}^{2} (6 - 6t) \, dt\]Using the power rule for integration, it becomes: \[(6t - 3t^2) \Big|_{1}^{2}\]Evaluating at the limits gives us:\[[(6(2) - 3(2)^2) - (6(1) - 3(1)^2)] = (12 - 12) - (6 - 3) = 0 - 3 = -3\]
03
Compute the Integral for \( \mathbf{j} \)-Component
The \( \mathbf{j} \)-component is \( 3\sqrt{t} \). This requires us to evaluate:\[\int_{1}^{2} 3\sqrt{t} \, dt = \int_{1}^{2} 3t^{1/2} \, dt\]Using the power rule for integration, we have:\[3 \cdot \frac{t^{3/2}}{3/2} \Big|_{1}^{2} = 2t^{3/2} \Big|_{1}^{2}\]Evaluating this gives:\[[2(2)^{3/2} - 2(1)^{3/2}] = [2 \times 2\sqrt{2} - 2 \times 1] = 4\sqrt{2} - 2\]
04
Compute the Integral for \( \mathbf{k} \)-Component
For the \( \mathbf{k} \)-component, the function is \( \frac{4}{t^2} \). We compute:\[\int_{1}^{2} \frac{4}{t^2} \, dt = \int_{1}^{2} 4t^{-2} \, dt\]Again, using the power rule, we find:\[4 \cdot \frac{t^{-1}}{-1} \Big|_{1}^{2} = -4t^{-1} \Big|_{1}^{2}\]Evaluating this gives:\[[-4(1/2) + 4(1)] = [-2 + 4] = 2\]
05
Combine Results for the Final Vector
Now that we have computed each component, we combine them to get the result of the integral vector:\[(-3) \mathbf{i} + (4\sqrt{2} - 2) \mathbf{j} + (2) \mathbf{k}\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vector Integration
Vector integration involves integrating each component of a vector function separately. When you are given a function in the form \[\int \left[ f(t) \mathbf{i} + g(t) \mathbf{j} + h(t) \mathbf{k} \right] dt\]this means that you'll integrate the function for each vector component:
- \[f(t)\] is integrated for the \(\mathbf{i}\) component.
- \[g(t)\] is integrated for the \(\mathbf{j}\) component.
- \[h(t)\] is integrated for the \(\mathbf{k}\) component.
- Evaluate each component's antiderivative at the upper and lower limits.
- Subtract the lower limit result from the upper limit for each component.
- Combine these results, maintaining the vector direction indicators.
Power Rule for Integration
The power rule for integration is a handy tool for integrating functions of the form \(x^n\). Specifically, it states:\[\int x^n \, dx = \frac{x^{n+1}}{n+1} + C\]for \(n eq -1\). Here, \(C\) is the constant of integration. This rule is straightforward to apply:
- Increase the exponent by one.
- Divide by the new exponent.
- Use the power rule on each vector component separately.
- Evaluate and subtract, respecting the vector's directional components.
Vector Function Components
When analyzing vector functions, it is essential to break them down into components aligned with \(\mathbf{i}, \mathbf{j},\) and \(\mathbf{k}\).Each component describes a part of the vector in a specific direction:
- The \(\mathbf{i}\)-component describes the direction along the x-axis.
- The \(\mathbf{j}\)-component describes the direction along the y-axis.
- The \(\mathbf{k}\)-component describes the direction along the z-axis.