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A spring of negligible mass has force constant \(k =\) 800 N/m. (a) How far must the spring be compressed for 1.20 J of potential energy to be stored in it? (b) You place the spring vertically with one end on the floor. You then lay a 1.60-kg book on top of the spring and release the book from rest. Find the maximum distance the spring will be compressed.

Short Answer

Expert verified
Compression for 1.20 J: 0.0546 m; Max compression with book: 0.0392 m.

Step by step solution

01

Understanding the Potential Energy Formula

The potential energy stored in a compressed spring is given by the formula \( PE = \frac{1}{2} k x^2 \), where \( PE \) is the potential energy, \( k \) is the spring constant, and \( x \) is the compression distance in meters. We need to calculate \( x \) for a potential energy of 1.20 J and \( k = 800 \text{ N/m} \).
02

Solving for Compression Distance (Part A)

Rearrange the formula \( PE = \frac{1}{2} k x^2 \) to solve for \( x \). This yields \( x = \sqrt{\frac{2 \times PE}{k}} \). Substituting the given values of \( PE = 1.20 \text{ J} \) and \( k = 800 \text{ N/m} \), we get \( x = \sqrt{\frac{2 \times 1.20}{800}} \). Simplify this to find \( x = \sqrt{\frac{2.4}{800}} \). Calculate to get \( x \approx 0.0546 \text{ meters} \).
03

Understanding Energy Conservation for Part B

When the book is placed on the spring and released, gravitational potential energy is converted to spring potential energy at maximum compression. Set gravitational potential energy \( mgh = \frac{1}{2} k x^2 \), where \( m = 1.60 \text{ kg} \), \( g = 9.8 \text{ m/s}^2 \), and \( h = x \) since the spring is compressed by height \( x \). Solve for \( x \) in \( 1.60 \times 9.8 \times x = \frac{1}{2} \times 800 \times x^2 \).
04

Solving for Maximum Compression (Part B)

Simplify the energy equation: \( 15.68x = 400x^2 \). Rearrange to solve for \( x \): \( 400x^2 - 15.68x = 0 \). Factor out \( x \): \( x(400x - 15.68) = 0 \). This gives solutions \( x = 0 \) or \( 400x = 15.68 \). Solving gives \( x = \frac{15.68}{400} \). Calculate \( x \approx 0.0392 \text{ meters} \).
05

Conclusion

In conclusion, the spring must be compressed approximately \( 0.0546 \text{ meters} \) for 1.20 J of potential energy, and the maximum distance it will be compressed by a 1.60 kg book is approximately \( 0.0392 \text{ meters} \).

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Key Concepts

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

Understanding the Spring Constant
The spring constant, symbolized as \( k \), is a measure of a spring's stiffness. It's defined as the force required to stretch or compress the spring by a unit distance. In our exercise, the spring constant is given as \( k = 800 \text{ N/m} \). This means it takes 800 Newtons of force to compress or extend the spring by a single meter. The higher the spring constant, the stiffer the spring is, and the more force is required for displacement. Understanding the spring constant is crucial for solving problems related to spring potential energy as it directly influences how much energy the spring can store. In formulas, it plays a key role in determining both potential energy stored and the compression distance of the spring.
Concept of Energy Conservation
Energy conservation is a fundamental principle stating that energy cannot be created or destroyed, only transformed from one form to another. In mechanical systems, this often involves converting between kinetic, potential, and elastic (spring) energy. In the given exercise, energy conservation helps us understand how the initial gravitational potential energy (when a book is held above the spring) is transformed into spring potential energy as the spring compresses. This conservation allows us to equate the potential energy due to gravity with the elastic potential energy of the spring at maximum compression, simplifying calculations and ensuring accuracy.
Calculating Compression Distance
Compression distance, denoted by \( x \), is an essential measurement in determining how much a spring is compressed or stretched. For a given amount of potential energy, the spring's compression distance can be calculated using the formula \( PE = \frac{1}{2} k x^2 \). By rearranging this formula, we solved for \( x \) to find how far the spring must be compressed to store 1.20 Joules of energy:\[ x = \sqrt{\frac{2 \times PE}{k}} \]Using the spring constant \( k = 800 \text{ N/m} \) and \( PE = 1.20 \text{ J} \), we get \( x \approx 0.0546 \text{ meters} \). This calculation shows that a small compression distance can correspond to a significant amount of stored energy, especially in springs with high spring constants like ours.
Explaining Gravitational Potential Energy
Gravitational potential energy (GPE) is the energy an object possesses due to its position in a gravitational field. It is given by the formula \( PE_{gravity} = mgh \), where \( m \) is the mass, \( g \) is the gravitational acceleration, and \( h \) is the height above a reference point. In the context of our exercise, when a book is placed on a vertically oriented spring, its GPE is converted to spring potential energy at maximum compression. The equation \( mgh = \frac{1}{2} k x^2 \) signifies this energy transformation. Given the book's mass of 1.60 kg, \( g = 9.8 \text{ m/s}^2 \), and equating this with the spring's energy equation, we determined the compression distance at maximum spring compression is approximately \( 0.0392 \text{ meters} \). Understanding GPE's role in this process helps clarify how potential energy is managed in mechanical systems and offers insight into designing practical applications.

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Most popular questions from this chapter

You are designing an amusement park ride. A cart with two riders moves horizontally with speed \(v = 6.00\) m/s. You assume that the total mass of cart plus riders is 300 kg. The cart hits a light spring that is attached to a wall, momentarily comes to rest as the spring is compressed, and then regains speed as it moves back in the opposite direction. For the ride to be thrilling but safe, the maximum acceleration of the cart during this motion should be 3.00\(g\). Ignore friction. What is (a) the required force constant of the spring, (b) the maximum distance the spring will be compressed?

A 2.50-kg mass is pushed against a horizontal spring of force constant 25.0 N/cm on a frictionless air table. The spring is attached to the tabletop, and the mass is not attached to the spring in any way. When the spring has been compressed enough to store 11.5 J of potential energy in it, the mass is suddenly released from rest. (a) Find the greatest speed the mass reaches. When does this occur? (b) What is the greatest acceleration of the mass, and when does it occur?

A spring stores potential energy \(U_0\) when it is compressed a distance \(x_0\) from its uncompressed length. (a) In terms of \(U_0\), how much energy does the spring store when it is compressed (i) twice as much and (ii) half as much? (b) In terms of \(x_0\), how much must the spring be compressed from its uncompressed length to store (i) twice as much energy and (ii) half as much energy?

A crate of mass \(M\) starts from rest at the top of a frictionless ramp inclined at an angle \(\alpha\) above the horizontal. Find its speed at the bottom of the ramp, a distance \(d\) from where it started. Do this in two ways: Take the level at which the potential energy is zero to be (a) at the bottom of the ramp with \(y\) positive upward, and (b) at the top of the ramp with y positive upward. (c) Why didn't the normal force enter into your solution?

A 62.0-kg skier is moving at 6.50 m/s on a frictionless, horizontal, snow- covered plateau when she encounters a rough patch 4.20 m long. The coefficient of kinetic friction between this patch and her skis is 0.300. After crossing the rough patch and returning to friction-free snow, she skis down an icy, frictionless hill 2.50 m high. (a) How fast is the skier moving when she gets to the bottom of the hill? (b) How much internal energy was generated in crossing the rough patch?

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