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A force of magnitude \(800.0 \mathrm{~N}\) stretches a certain spring by \(0.200 \mathrm{~m}\) from its equilibrium position. (a) What is the force constant of this spring? (b) How much elastic potential energy is stored in the spring when it is: (i) stretched \(0.300 \mathrm{~m}\) from its equilibrium position and(ii) compressed by \(0.300 \mathrm{~m}\) from its equilibrium position? (c) How much work was done in stretching the spring by the original \(0.200 \mathrm{~m} ?\)

Short Answer

Expert verified
(a) 4000.0 N/m, (b) 180.0 J (both stretched or compressed 0.300 m), (c) 80.0 J

Step by step solution

01

Understand Hooke's Law

The force required to stretch or compress a spring by a distance \( x \) from its equilibrium position is given by Hooke's Law: \( F = kx \), where \( F \) is the force applied, \( x \) is the displacement, and \( k \) is the spring constant.
02

Calculate the force constant

Given that a force of 800.0 N stretches the spring by 0.200 m, we can use Hooke's Law to find the spring constant \( k \). \[ k = \frac{F}{x} = \frac{800.0 \text{ N}}{0.200 \text{ m}} = 4000.0 \text{ N/m} \].
03

Recognize the formula for elastic potential energy

The elastic potential energy stored in a spring displaced from equilibrium by \( x \) is given as: \( U = \frac{1}{2} k x^2 \).
04

Calculate elastic potential energy when stretched 0.300 m

Use the formula for elastic potential energy to calculate the energy when the spring is stretched by 0.300 m. \[ U = \frac{1}{2} \cdot 4000.0 \text{ N/m} \cdot (0.300 \text{ m})^2 = 180.0 \text{ J} \].
05

Calculate elastic potential energy when compressed 0.300 m

The potential energy formula applies to both compression and stretching. For a 0.300 m compression: \[ U = \frac{1}{2} \cdot 4000.0 \text{ N/m} \cdot (0.300 \text{ m})^2 = 180.0 \text{ J} \].
06

Calculate work done in stretching 0.200 m

The work done in stretching or compressing a spring by \( x \) is equal to the elastic potential energy stored when the spring is displaced. For a stretch of 0.200 m: \[ W = \frac{1}{2} k x^2 = \frac{1}{2} \cdot 4000.0 \text{ N/m} \cdot (0.200 \text{ m})^2 = 80.0 \text{ J} \].

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Key Concepts

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

Understanding the Force Constant
The "force constant," also known as the "spring constant," is a key parameter defining a spring's stiffness. According to Hooke's Law, the force required to compress or stretch a spring is directly proportional to the displacement of the spring. This relationship is expressed by the equation \( F = kx \). Here, \( F \) stands for the force applied, \( x \) is the displacement from the spring's equilibrium position, and \( k \) is the spring constant.

The force constant \( k \) has units of N/m (newtons per meter), which illustrates how much force is needed to elongate or compress the spring by one meter. In our exercise, a force of 800.0 N stretches the spring by 0.200 m.

By rearranging Hooke's Law, we find \( k = \frac{F}{x} \). Substituting in the given values:
  • \( F = 800.0 \text{ N} \)
  • \( x = 0.200 \text{ m} \)
This gives us \( k = 4000.0 \text{ N/m} \). A high force constant implies a stiffer spring, requiring more force to achieve the same displacement.
Elastic Potential Energy in Springs
When a spring is either stretched or compressed, it stores energy called elastic potential energy. The amount of this energy can be calculated using the formula \( U = \frac{1}{2} k x^2 \). In this formula, \( U \) represents the elastic potential energy, \( k \) is the spring constant, and \( x \) is the displacement from the equilibrium position.

Elastic potential energy increases with greater displacements and stiffer springs (higher \( k \)). In our scenario, the spring constant \( k \) was previously calculated as 4000.0 N/m. To find the potential energy for a displacement of 0.300 m, we substitute:

  • \( U = \frac{1}{2} \times 4000.0 \text{ N/m} \times (0.300 \text{ m})^2 \)
  • Results in \( U = 180.0 \text{ J} \) both when stretched or compressed by 0.300 m
This indicates that the energy stored depends solely on the magnitude of displacement, not the direction of the displacement.
Work Done on a Spring
The work done on a spring when stretching or compressing it refers to the energy transferred into the spring to change its length. This work is equal to the elastic potential energy stored in the spring for a given displacement. Using the formula \( W = \frac{1}{2} k x^2 \), where \( W \) represents the work done, we can determine the energy needed for a specific displacement.

In our exercise, calculating the work done for a 0.200 m stretch involves substituting the known values into the equation:

  • \( W = \frac{1}{2} \times 4000.0 \text{ N/m} \times (0.200 \text{ m})^2 \)
  • This yields \( W = 80.0 \text{ J} \).
This computation shows how the integral of force over the distance traveled results in the amount of work done, transforming it into stored elastic potential energy.

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Most popular questions from this chapter

You throw a \(20 \mathrm{~N}\) rock into the air from ground level and observe that, when it is \(15.0 \mathrm{~m}\) high, it is traveling upward at \(25.0 \mathrm{~m} / \mathrm{s}\). Use the work-energy theorem to find (a) the rock's speed just as it left the ground and (b) the maximum height the rock will reach.

A spring with spring constant \(k\) is anchored to the wall on one side of a hockey rink. A hockey puck is pressed against the spring and then released to slide across the ice. In the process the hockey puck gains a kinetic energy \(K .\) Derive an expression for the initial compression of the spring \(x\) in terms of \(k\) and \(K\).

A certain spring stores \(10.0 \mathrm{~J}\) of potential energy when it is stretched by \(2.00 \mathrm{~cm}\) from its equilibrium position. (a) How much potential energy would the spring store if it were stretched an additional \(2.00 \mathrm{~cm} ?\) (b) How much potential energy would it store if it were compressed by \(2.00 \mathrm{~cm}\) from its equilibrium position? (c) How far from the equilibrium position would you have to stretch the string to store \(20.0 \mathrm{~J}\) of potential energy? (d) What is the force constant of this spring?

The total height of Yosemite Falls is \(2425 \mathrm{ft}\). (a) How many more joules of gravitational potential energy are there for each kilogram of water at the top of this waterfall compared with each kilogram of water at the foot of the falls? (b) Find the kinetic energy and speed of each kilogram of water as it reaches the base of the waterfall, assuming that there are no losses due to friction with the air or rocks and that the mass of water had negligible vertical speed at the top. How fast (in \(\mathrm{m} / \mathrm{s}\) and \(\mathrm{mph}\) ) would a \(70 \mathrm{~kg}\) person have to run to have that much kinetic energy? (c) How high would Yosemite Falls have to be so that each kilogram of water at the base had twice the kinetic energy you found in part (b); twice the speed you found in part (b)?

Ski jump ramp. You are designing a ski jump ramp for the next Winter Olympics. You need to calculate the vertical height \(h\) from the starting gate to the bottom of the ramp. The skiers push off hard with their ski poles at the start, just above the starting gate, so they typically have a speed of \(2.0 \mathrm{~m} / \mathrm{s}\) as they reach the gate. For safety, the skiers should have a speed of no more than \(30.0 \mathrm{~m} / \mathrm{s}\) when they reach the bottom of the ramp. You determine that for an \(85.0 \mathrm{~kg}\) skier with good form, friction and air resistance will do total work of magnitude \(4000 \mathrm{~J}\) on him during his run down the slope. What is the maximum height \(h\) for which the maximum safe speed will not be exceeded?

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