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A particle is taken from point \(A\) to point \(B\) under the influence of a force field. Now it is taken back from \(B\) to \(A\) and it is observed that the work done in taking the particle from \(A\) to \(B\) is not equal to the work done in taking it from \(B\) to \(A\). If \(W_{n c}\) and \(W_{c}\) are the work done by non- conservative and conservative forces present in the system, respectively \(\Delta U\) is the change in potential energy and \(\Delta k\) is the chan in kinetic energy, then (1) \(W_{n c}-\Delta U=\Delta k\) (2) \(W_{e}=-\Delta U\) (3) \(W_{n c}^{n}+W_{c}=\Delta k\) (4) \(W_{n c}-\Delta U=-\Delta k\)

Short Answer

Expert verified
Option (1): \(W_{n c} - \Delta U = \Delta k\).

Step by step solution

01

Understand the Problem

The problem involves moving a particle between two points under the influence of a force field, with varying work done in each direction. This implies the presence of non-conservative forces since the work done is path-dependent.
02

Recall the Work-Energy Principle

The work-energy principle states that the work done by all forces is equal to the change in kinetic energy. For a system involving conservative and non-conservative forces, the equation is: \( W_{c} + W_{n c} = \Delta K \).
03

Understand Change in Potential Energy

The change in potential energy (\( \Delta U \)) is related to the work done by conservative forces. For conservative forces, \( W_{c} = -\Delta U \).
04

Apply the Equation of Motion

For a system with non-conservative forces, the equation becomes: \( W_{n c} + W_{c} = \Delta K \). Since \( W_{c} = -\Delta U \), it can be rearranged to: \( W_{n c} - \Delta U = \Delta K \).
05

Match Solution with Provided Options

From the rearranged equation \( W_{n c} - \Delta U = \Delta K \), it matches option (1).

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Key Concepts

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

Non-conservative forces
Non-conservative forces are forces for which the work done depends on the path taken between two points. Common examples of non-conservative forces include friction and air resistance. These forces dissipate energy, typically as heat, which is why the work done often varies between different paths for the same start and end points.
This path dependency implies that the energy used is not entirely conserved within mechanical systems, as energy is lost rather than merely transferred between kinetic and potential forms. This results in differing amounts of work being done on a particle when moving back and forth along the same path under a non-conservative force field.
When solving physics problems, recognizing the presence of non-conservative forces can help you understand why the work done may not be consistent, and it is crucial when applying the work-energy principle in these scenarios. This influences not only the energy calculations but also the understanding of energy conservation limits in the given problem.
Conservative forces
Conservative forces, unlike non-conservative forces, have work that is path-independent. This means that the work done by conservative forces between two points only depends on these points' positions, not the trajectory taken.
Common examples include gravitational and spring forces. The hallmark of conservative forces is energy conservation, where energy can be fully converted between kinetic and potential forms without any loss to the environment. Thus, the total mechanical energy (kinetic + potential) remains constant in a system where only conservative forces are doing work.
In mathematical terms, if only conservative forces are acting on a system, the work done by these forces equals the negative change in potential energy: \( W_c = -\Delta U \). Understanding this principle allows you to solve problems where energy conservation is applicable, simplifying the calculations involved.
Potential energy change
Potential energy is the energy stored in a system due to its position in a force field. For conservative forces, changes in potential energy reflect the work done by the force.
The change in potential energy (\(\Delta U\)) between two points in a conservative force field is equal to the negative of the work done by these forces. For instance, in a gravitational field, the potential energy increases as an object is lifted against gravity, and decreases when it falls.
Mathematically, for any conservative force, this relationship can be expressed as: \( W_c = -\Delta U \). This is useful for calculating energy transformations, as it accounts for how mechanical energy transitions between kinetic and potential forms without net loss to other forms, thus applying in various physics problems
where energy conservation is key. Understanding potential energy changes is crucial when analyzing the work done in systems with both conservative and non-conservative forces.

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Most popular questions from this chapter

A block of mass \(m\) lies on a wedge of mass \(M\). The wedge in tum lies on a smooth horizontal surface. Friction is absent everywhere. The wedge-block system is released from rest. All situations given in Column I are to be estimated in duration the block undergoes a vertical displacement \(h\) starting from rest. Match the statements in Column I with the results in Column II. ( \(g\) is acceleration due to gravity.) $$ \begin{array}{|c|c|} \hline {\begin{array}{c} \text { Column I } \\ \end{array}} & {\begin{array}{c} \text { Column II } \\ \end{array}} \\ \hline \text { i. } \text {Work done by normal reaction acting on the block is} & \text { a. } \text{positive} \\ \hline \text { ii. } \text{Work done by normal reaction (exerted by block) acting on the wedge is} & \text { b. } \text{negative} \\ \hline \text { iii. } \text{The sum of work done by normal reaction on the block and work done by normal on wedge} & \text { c. } \text{Zero}\\\ \hline \text { iv. } \text{Net work done by all forces on the block is} & \text { d. } \text{less than \(m g h\) in magnitude} \\ \hline \end{array} $$

A system consists of two identical cubes, each of mass \(3 \mathrm{~kg}\), linked together by a compressed weightless spring of force constant \(1000 \mathrm{~N} \mathrm{~m}^{-1}\). The cubes are also connected by a thread which is burnt at a certain moment. At what minimum value of initial compression \(x_{0}\) (in \(\mathrm{cm}\) ) of the spring will the lower cube bounce up after the thread is burnt through?

A block of mass \(1 \mathrm{~kg}\) is pressed against a spring of constant \(400 \mathrm{~N} / \mathrm{m}\). The spring is compressed by \(10 \mathrm{~cm}\) and block is released. Which of the following is a possible velocity of the block during subsequent motion? (1) \(2 \mathrm{~m} / \mathrm{s}\) (2) \(1 \mathrm{~m} / \mathrm{s}\) (3) \(3 \mathrm{~m} / \mathrm{s}\) (4) \(4 \mathrm{~m} / \mathrm{s}\)

A car drives along a straight level frictionless road by an engine delivering constant power. Then velocity is directly proportional to \(\begin{array}{ll}\text { (1) } t & \text { (2) } \frac{1}{\sqrt{t}}\end{array}\) (3) \(\sqrt{t}\) (4) None of these

A particle of mass \(m\) moves with a variable velocity \(v\), which changes with distance covered \(x\) along a straight line as \(v=k \sqrt{x}\), where \(k\) is a positive constant. The work done by all the forces acting on the particle, during the first \(t\) seconds is (l) \(\frac{m k^{4}}{t^{2}}\) (2) \(\frac{m k^{4} t^{2}}{4}\) (3) \(\frac{m k^{4} t^{2}}{8}\) (4) \(\frac{m k^{4} t^{2}}{16}\)

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