Chapter 6: Problem 6
For a certain type of nonlinear spring, the force required to keep the spring stretched a distance \(s\) is given by the formula \(F=k s^{4 / 3}\). If the force required to keep it stretched 8 inches is 2 pounds, how much work is done in stretching this spring 27 inches?
Short Answer
Expert verified
The work done to stretch the spring 27 inches is approximately 117.16 inch-pounds.
Step by step solution
01
Understand the formula for force
The force required to stretch the spring is given by the formula \(F = k s^{4/3}\), where \(F\) is the force, \(k\) is a constant, and \(s\) is the distance stretched.
02
Determine the constant \(k\)
We know \(F = 2\) pounds when \(s = 8\) inches. Substitute these values into the force equation: \[ 2 = k \cdot 8^{4/3} \]Solve for \(k\):\[ k = \frac{2}{8^{4/3}} \] Calculate \(8^{4/3}\), which is \( (2^3)^{4/3} = 2^4 = 16 \), hence:\[ k = \frac{2}{16} = \frac{1}{8} \].
03
Write the force function with \(k\)
Now that we have \(k = \frac{1}{8}\), substitute \(k\) back into the force equation:\[ F(s) = \frac{1}{8} s^{4/3} \].
04
Set up the integral for work done
Work done by a force is the integral of the force function with respect to distance. We need to calculate work done to stretch the spring from 0 to 27 inches:\[ W = \int_{0}^{27} \frac{1}{8} s^{4/3} \, ds \].
05
Compute the integral
To find the integral, compute:\[ W = \frac{1}{8} \int_{0}^{27} s^{4/3} \, ds \].The antiderivative of \(s^{4/3}\) is \(\frac{s^{7/3}}{7/3} = \frac{3}{7} s^{7/3}\). Therefore,\[ W = \frac{1}{8} \left[ \frac{3}{7} s^{7/3} \right]_{0}^{27} \].Evaluate this from 0 to 27:\[ W = \frac{1}{8} \times \frac{3}{7} \left[ 27^{7/3} - 0^{7/3} \right] \].
06
Evaluate \( 27^{7/3} \)
Compute \( 27^{7/3} \):\( 27^{7/3} = (3^3)^{7/3} = 3^7 \). Thus, \( 3^7 = 2187 \).
07
Calculate the work done
Substitute back \( 2187 \) for \(27^{7/3}\) in the equation for work:\[ W = \frac{1}{8} \times \frac{3}{7} \times 2187 \].Simplify:\[ W = \frac{6561}{56} = 117.1607 \] approximately.The work done is approximately 117.16 inch-pounds.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Nonlinear Springs
Nonlinear springs differ from ordinary linear springs by having a force that does not increase proportionally with the distance they are stretched. Instead, the force they exert follows a nonlinear pattern. In the given exercise, the force is expressed by the formula:
- \( F = k s^{4/3} \)
- Where \( F \) is the force, \( s \) is the distance the spring is stretched, and \( k \) is a constant unique to that particular spring.
Work and Energy in Physics
In physics, work refers to the energy transferred when an object is moved over a distance by an external force. The formula to calculate work is the integral of force over the distance it acts upon:
- \( W = \int F(s) \, ds \)
- Where \( W \) is the work done, \( F(s) \) is the force as a function of distance \( s \), and \( s \) itself can vary over the path defined by the integral limits.
Integration Techniques
Integration is a fundamental calculus tool used to find the work done by nonlinear springs, as seen with the function given \( F(s) = \frac{1}{8} s^{4/3} \). Calculating work requires performing definite integrals:
- The integral \( \int_{0}^{27} s^{4/3} \, ds \) calculates the net work done for stretching from 0 to 27 inches.
- The antiderivative or the result of integrating \( s^{4/3} \) is \( \frac{3}{7} s^{7/3} \), emphasizing the need to have a strong grasp of integral calculus.