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\(\bullet\) \(\bullet\) An unstretched spring has a force constant of 1200 \(\mathrm{N} / \mathrm{m}\) . How large a force and how much work are required to stretch the spring: (a) by 1.0 \(\mathrm{m}\) from its unstretched length, and (b) by 1.0 \(\mathrm{m}\) beyond the length reached in part (a)?

Short Answer

Expert verified
(a) 1200 N and 600 J; (b) 2400 N and 1800 J.

Step by step solution

01

Understanding Hooke's Law

A spring force follows Hooke's Law, which states that the force needed to stretch or compress a spring by a distance \( x \) is proportional to that distance. The formula is \( F = kx \), where \( k \) is the spring constant and \( x \) is the displacement from the equilibrium position.
02

Calculating Force for Part (a)

To find the force required to stretch the spring by 1.0 m from its unstretched length, use Hooke's Law: \( F = kx \). Given \( k = 1200 \, \mathrm{N/m} \) and \( x = 1.0 \, \mathrm{m} \), the calculation is \( F = 1200 \times 1.0 = 1200 \, \mathrm{N} \).
03

Calculating Work for Part (a)

The work done on a spring is given by the formula \( W = \frac{1}{2} k x^2 \). With \( k = 1200 \, \mathrm{N/m} \) and \( x = 1.0 \, \mathrm{m} \), the work done is \( W = \frac{1}{2} \times 1200 \times (1.0)^2 = 600 \, \mathrm{J} \).
04

Calculating Force for Part (b)

For part (b), the spring is stretched an additional 1.0 m beyond the length reached in part (a), so \( x = 2.0 \, \mathrm{m} \). Using Hooke's Law: \( F = 1200 \times 2.0 = 2400 \, \mathrm{N} \).
05

Calculating Work for Part (b)

The work needed for additional 1.0 m stretch beyond part (a) can be found by subtracting the total work from the work done in part (a). The total work for 2.0 m is \( W = \frac{1}{2} \times 1200 \times (2.0)^2 = 2400 \, \mathrm{J} \). So, \( W_{\mathrm{additional}} = 2400 - 600 = 1800 \, \mathrm{J} \).

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Key Concepts

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

Spring Force
When you stretch or compress a spring, you're engaging with the spring force, a concept rooted in Hooke's Law. This law expresses a simple yet powerful idea: the force exerted by a spring is directly proportional to the displacement from its original position. In mathematical terms, it's represented as: \( F = kx \).
Here, \( F \) is the spring force, \( k \) is the spring constant, and \( x \) is the displacement. The spring constant \( k \) is a measure of the stiffness of the spring: a higher \( k \) means a stiffer spring that needs more force to stretch or compress.
This means if you stretch a spring by 1 meter, and \( k = 1200 \, \text{N/m} \), the force required is \( 1200 \, \text{N} \). If you double the distance to 2 meters, you double the force to \( 2400 \, \text{N} \). Remember, the direction of the force always opposes the direction of the stretch or compression.
Spring Constant
The spring constant, denoted by \( k \), is a fundamental characteristic of a spring that dictates its stiffness. Quite simply, it describes how resistant a spring is to being compressed or stretched. A spring with a high \( k \) requires much more force to achieve a certain amount of stretch compared to a spring with a low \( k \).
In practical applications, like the exercise given, knowing the spring constant allows you to predict how a spring will behave under various loads. For instance, the spring constant of 1200 \( \text{N/m} \) in our problem indicates that for every meter of stretch, a 1200 Newton force is exerted by the spring. This is pivotal in designing systems that rely on springs, such as vehicle suspension systems and mechanical scales.
Understanding the spring constant helps in selecting the right spring for your needs, ensuring it neither stretches too easily nor refuses to budge under intended conditions.
Work on a Spring
Work done on a spring involves changing its length by stretching or compressing it. The work measures the energy transferred to the spring to change its position. Formulaically, the work \( W \) done on a spring is calculated as: \( W = \frac{1}{2}kx^2 \).
This equation shows that work is dependent on both the spring constant \( k \) and the square of the displacement \( x \). For example, stretching the given spring by 1 meter requires \( 600 \, \text{J} \) of work. If the displacement doubles to 2 meters, the work quadruples to \( 2400 \, \text{J} \), illustrating the quadratic relationship.
It's important to note that this work is stored as potential energy within the spring, which can later be released to perform tasks, like pushing back against the force applied. By understanding how work on a spring functions, you can better appreciate the energy dynamics involved in spring-based systems.

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Most popular questions from this chapter

\(\bullet\) \(\bullet\) At 7.35 cents per kilowatt-hour, (a) what does it cost to operate a 10.0 hp motor for 8.00 hr? (b) What does it cost to leave a 75 W light burning 24 hours a day?

\(\bullet\) Bumper guards. You are asked to design spring bumpers for the walls of a parking garage. A freely rolling 1200 \(\mathrm{kg}\) car moving at 0.65 \(\mathrm{m} / \mathrm{s}\) is to compress the spring no more than 7.0 \(\mathrm{cm}\) before stopping. (a) What should be the force constant of the spring, and what is the maximum amount of energy that gets stored in it? (b) If the springs that are actually delivered have the proper force constant but can become compressed by only \(5.0 \mathrm{cm},\) what is the maximum speed of the given car for which they will provide adequate protection?

\(\bullet\) A tandem (two-person) bicycle team must overcome a force of 165 \(\mathrm{N}\) to maintain a speed of 9.00 \(\mathrm{m} / \mathrm{s}\) . Find the power required per rider, assuming that each contributes equally.

\(\bullet\) \(\bullet\) Food calories. The food calorie, equal to \(4186 \mathrm{J},\) is a measure of how much energy is released when food is metabo- lized by the body. A certain brand of fruit-and-cereal bar con- tains 140 food calories per bar. (a) If a 65 \(\mathrm{kg}\) hiker eats one of these bars, how high a mountain must he climb to "work off" the calories, assuming that all the food energy goes only into increasing gravitational potential energy? (b) If, as is typical, only 20\(\%\) of the food calories go into mechanical energy, what would be the answer to part (a)? (Note: In this and all other problems, we are assuming that 100\(\%\) of the food calories that are eaten are absorbed and used by the body. This actually not true. A person's "metabolic efficiency" is the percentage of calories eaten that are actually used; the rest are eliminated by the body. Metabolic efficiency varies considerably from person to person.)

\(\bullet\) While a roofer is working on a roof that slants at \(36^{\circ}\) above the horizontal, he accidentally nudges his 85.0 N toolbox, causing it to start sliding downward, starting from rest. If it starts 4.25 \(\mathrm{m}\) from the lower edge of the roof, how fast will the toolbox be moving just as it reaches the edge of the roof if the kinetic friction force on it is 22.0 \(\mathrm{N} ?\)

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