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Solve the given problems by determinants. In Exerciser-46,\( set up appropriate systems of equations. All numbers are accurate to at least two significant digits. In a laboratory experiment to measure the acceleration of an object, the distances traveled by the object were recorded for three different time intervals. These data led to the following equations: $$\begin{array}{l} s_{0}+2 v_{0}+2 a=20 \\ s_{0}+4 v_{0}+8 a=54 \\ s_{0}+6 v_{0}+18 a=104 \end{array}$$ Here, \)s_{0}\( is the initial displacement (in \)\mathrm{ft}\( ), \)v_{0}\( is the initial velocity (in \)\mathrm{ft} / \mathrm{s}\( ), and \)a\( is the acceleration (in \)\mathrm{ft} / \mathrm{s}^{2}\( ). Find \)s_{0}, v_{0},\( and \)a$

Short Answer

Expert verified
The values are \(s_{0} = 31\) ft, \(v_{0} = -82.5\) ft/s, \(a = -10\) ft/s².

Step by step solution

01

Set up the coefficient matrix

Given the system of equations, we can write:\[\begin{align*}s_{0} + 2v_{0} + 2a &= 20 \s_{0} + 4v_{0} + 8a &= 54 \s_{0} + 6v_{0} + 18a &= 104 \\end{align*}\]The coefficient matrix is then:\[A = \begin{bmatrix}1 & 2 & 2 \1 & 4 & 8 \1 & 6 & 18\end{bmatrix}\]
02

Form the constant matrix

The constants from the right side of the equations form the constant matrix:\[b = \begin{bmatrix}20 \54 \104\end{bmatrix}\]
03

Calculate the determinant of the coefficients

To solve using determinants (Cramer's Rule), first calculate the determinant of the matrix A:\[\det(A) = \begin{vmatrix} 1 & 2 & 2 \1 & 4 & 8 \1 & 6 & 18 \end{vmatrix} = 1(4 \cdot 18 - 8 \cdot 6) - 2(1 \cdot 18 - 8 \cdot 1) + 2(1 \cdot 6 - 4 \cdot 1)\]= 1(72 - 48) - 2(18 - 8) + 2(6 - 4)= 24 - 20 + 4 = 8.
04

Form the matrix for s_0 and calculate determinant

Replace the first column of matrix A with the constant matrix b and calculate the determinant:\[A_{s_{0}} = \begin{bmatrix}20 & 2 & 2 \54 & 4 & 8 \104 & 6 & 18\end{bmatrix}\]\[\det(A_{s_{0}}) = \begin{vmatrix} 20 & 2 & 2 \54 & 4 & 8 \104 & 6 & 18 \end{vmatrix} = 20(4 \cdot 18 - 8 \cdot 6) - 2(54 \cdot 18 - 8 \cdot 104) + 2(54 \cdot 6 - 4 \cdot 104)\]= 20 \times 24 - 2 \times 232 + 2 \times 116= 480 - 464 + 232= 248.
05

Solve for s_0

Using Cramer's Rule, solve for \(s_{0}\) using the determinants:\[s_{0} = \frac{\det(A_{s_{0}})}{\det(A)} = \frac{248}{8} = 31.\]
06

Form the matrix for v_0 and calculate determinant

Replace the second column of matrix A with the constant matrix b and calculate the determinant:\[A_{v_{0}} = \begin{bmatrix}1 & 20 & 2 \1 & 54 & 8 \1 & 104 & 18\end{bmatrix}\]\[\det(A_{v_{0}}) = \begin{vmatrix} 1 & 20 & 2 \1 & 54 & 8 \1 & 104 & 18 \end{vmatrix} = 1(54 \cdot 18 - 8 \cdot 104) - 20(1 \cdot 18 - 8 \cdot 1) + 2(1 \cdot 104 - 54 \cdot 1)\]= 1 \times -560 - 20 \times 10 + 2 \times 50= -560 - 200 + 100= -660.
07

Solve for v_0

Using Cramer's Rule, solve for \(v_{0}\) using the determinants:\[v_{0} = \frac{\det(A_{v_{0}})}{\det(A)} = \frac{-660}{8} = -82.5.\]
08

Form the matrix for a and calculate determinant

Replace the third column of matrix A with the constant matrix b and calculate the determinant:\[A_{a} = \begin{bmatrix}1 & 2 & 20 \1 & 4 & 54 \1 & 6 & 104\end{bmatrix}\]\[\det(A_{a}) = \begin{vmatrix} 1 & 2 & 20 \1 & 4 & 54 \1 & 6 & 104 \end{vmatrix} = 1(4 \cdot 104 - 54 \cdot 6) - 2(1 \cdot 104 - 54 \cdot 1) + 20(1 \cdot 6 - 4 \cdot 1)\]= 1 \times -20 - 2 \times 50 + 20 \times 2= -20 - 100 + 40= -80.
09

Solve for a

Using Cramer's Rule, solve for \(a\) using the determinants:\[a = \frac{\det(A_{a})}{\det(A)} = \frac{-80}{8} = -10.\]
10

Conclusion: Final Values

The initial displacement \(s_{0}\) is 31 ft, the initial velocity \(v_{0}\) is -82.5 ft/s, and the acceleration \(a\) is -10 ft/s².

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Cramer's Rule
Cramer's Rule is a method to solve a system of linear equations with as many equations as variables. It uses determinants, which are special numbers calculated from a matrix, to find the solutions of each variable. The process involves replacing one column of the matrix at a time with the constant terms and calculating the determinant of this new matrix. Then, dividing this determinant by the determinant of the original coefficient matrix provides a solution for the variable in question. This method is especially useful for small systems because of its straightforward application. However, for larger systems, other methods might be more efficient due to computing complexity. To use Cramer's Rule, make sure:
  • The system of equations has the same number of equations as unknowns.
  • The determinant of the coefficient matrix is not zero; otherwise, Cramer's Rule cannot be applied, indicating no unique solution.
System of Equations
A system of equations is a set of two or more equations that have common variables. Solving these equations means finding the values of these variables that satisfy all the equations simultaneously. Systems can be consistent, with one solution, infinitely many solutions, or none at all if they are inconsistent. To solve them, methods like graphing, substitution, elimination, and matrix methods such as Cramer's Rule or Gaussian elimination can be used. In this specific exercise, the system comprises three equations representing relationships between physical quantities: initial displacement, initial velocity, and acceleration. Depending on the method chosen, equations are either manipulated algebraically to find solutions, or matrix theory is applied to solve them efficiently.
Matrix Solution
A matrix solution involves representing a system of equations as a matrix equation. This format is particularly useful because it allows us to employ linear algebra techniques to find solutions. The general representation of a system as a matrix equation is in the form \(AX = B\), where \(A\) is the coefficient matrix of the variables, \(X\) is the column matrix of unknowns, and \(B\) is the constant matrix.When solving using the matrix method, one common approach is to find the inverse of the coefficient matrix \(A\), provided that it exists, and use it to compute the solution: \X = A^{-1}B\. If using determinants, Cramer’s Rule, which is the focus here, is preferred for smaller systems as it directly uses the matrix determinants to find each variable.The advantage of matrix solutions includes a structured format and the ability to handle large systems effectively with computational tools.
Acceleration Calculation
Acceleration is a key concept in physics that describes the rate of change of velocity of an object. It is a vector quantity, meaning it has both magnitude and direction. In our system of equations, the variable 'a' represents acceleration and is calculated in feet per second squared \(ft/s^2\).The significance of solving for acceleration in this context is determining how quickly an object's velocity changes over time based on the initial conditions and distances traveled at specific time intervals. Calculating acceleration accurately is critical in experimental physics as it can influence the understanding of an object's motion and applicable laws of physics.To find the acceleration using the system provided, you derive the variable's solution using matrix approaches like Cramer's Rule, ensuring that the setup equations accurately reflect the physical understanding of the motion involved.

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Most popular questions from this chapter

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