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Questions tagged [work]

The product of the force on an object and the displacement the object undergoes along the direction of the force.

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Solving for work without being given pressure

The following is an MCAT question I'm not sure how to approach. We have to solve for work without being given pressure. This is how far I've gotten: F=PA, Thus, W=Fd, W=PAd. Ad=deltaV, so W=PdeltaV. ...
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4answers
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Why there is a negative sign in the formula of calculating work done in electrostatics?

$$W = - \int _ { a } ^ { b } \vec { F } \cdot d \vec { r }$$ ( from The Feynman lectures on physics vol. 2, new millennium edition, page 4-4) In this formula why there is a negative sign in the ...
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1answer
33 views

Meaning of “a force that derives from potential energy”

In mechanics course, when the idea of equilibrium was introduced they included the idea of a force that derives from potential energy which is the force $F$ which is related to the potential energy $...
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Work of centrifugal force cartesian coordinates

Hey I have a question about an expression in the textbook of Born. There a pendulum of variable is considered. Then it is stated that for shortening a work given by \begin{equation} -ml \int \dot{\phi}...
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1answer
29 views

Work done in moving a charge in circuit?

Why is the work done in moving a charge from one point to another in a circuit through any path the same even though heat and other losses are there?
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+50

Unrelated states in virtual work

I'm reading the Wikipedia article on virtual work, and there is the following quote: Consider now the free body diagram of a deformable body, which is composed of an infinite number of differential ...
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55 views

Work done by battery?

Why the work done by a battery is Q*V where V is emf of battery and Q is charge that is made to flow in circuit?please explain detail? explain and write the formulas
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6answers
535 views

Why the work done is positive when bringing 2 opposite charges together?

we know that if the applied force is in the direction of the displacement then work done is positive.But in case of bringing 2 opposite charges from infinite to a certain distance,the work done is ...
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1answer
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Displacement due to same force on different surfaces [closed]

If a force of 10N is applied to an object on surface1, the displacement is 10m. If the same force is applied on them same object but on surface2, then the displacement is 20m. How can the work done be ...
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Question on energy and momentum [closed]

A thin light inextensible frictionless cord of length "L" wearing a small bead is tied between two nails that are in the same level a distance "0.5 L" apart. Initially the bead is held close to a nail ...
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1answer
34 views

The work due to friction given an influential force

Statement: I am trying to work through Chapter 8, Problem #70 of OpenStax University Physics Volume 1 and I cannot figure out what I'm doing wrong. The problem statement is as follows: A particle of ...
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2answers
47 views

Apparent work energy paradox

The diagram shows a block of mass M with two rocket engines of negligible mass attached to it (pointed in opposite directions) and producing 5N of thrust each. Consider two cases where the mass is ...
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2answers
60 views

Why is work done a dot product of force and distance?

Suppose force is applied on an object at an angle theta and the block moves for some distance along x axis I understand that we take x component of ...
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1answer
18 views

Work done and change in mechanical energy

I have a hard time understanding the equation $W_{Driving} +W_{Friction} = \Delta E_{mechanical}$ Is there any derivation of it?
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4answers
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Why $dW=pdV$ is an inexact differential?

I remember an exact differential as: $$A=M(x,y)dx+N(x,y)dy $$ and the condition for be exact is: $$\frac{\partial M}{\partial y}=\frac{\partial N}{\partial x}. $$ Can I use that definition to ...
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2answers
37 views

Applying external force on test charge greater than repulsive force of electric field

In the textbook, it is written that only that amount of external force is applied that balances the repulsive force of the electric field without producing acceleration. Without acceleration, is it ...
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4answers
111 views

Why is the work done by tension in a pulley always zero?

Consider a pulley with a rope around it connecting two masses. According to this post the work done by the rope on the two mass system is 0. The explanation of this post makes sense to me; the blocks ...
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3answers
93 views

Work and energy - explanation of definition [duplicate]

I have a question about the definition of energy. the definition is "ability to do work". what does it mean? what is the ability that the definition talks about? what is the meaning of ability in ...
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2answers
74 views

Maximum work done in isothermal or isobaric process? [on hold]

In an isothermal process all heat is converted into work while in an isobaric process heat is converted into work as well as internal energy. However, the PV-graph shows that the maximum work is done ...
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1answer
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Electric Potential: Building system of point charges

How can we prove that the amount of work we have to do to build a system of point charges is same , whether we place the point charges one by one or all at once
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2answers
36 views

Calculating work done in Thermodynamics

Unless I am mistaken, to find the work done going from Point $1$ to Point $2$, the textbook noted I needed to find the area under the curve of the region in blue. However, if I'm meant to find the ...
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1answer
40 views

Derive electrical power from electrical work

I am a little confused with some aspects of electrical power and electrical work. The example is connected to a thermodynamic problem: Consider an adiabatic vessel filled with an arbitrary fluid. ...
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4answers
100 views

Direction of $d\mathbf{l}$

A solid sphere has charge $q$ and radius $R$. Find the potential at a point a distance $r$ from the center of the sphere where $r>R$, using infinity as the reference point. My attempt: From Gauss'...
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Sign in $\Delta U= -\int\vec{F}\cdot d\vec{l}$

So I have been trying to understand why there is a negative sign in the following$\Delta U= -\int\vec{F}\cdot d\vec{l}$ I wanted to try to understand it by trying to derive the gravitational ...
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3answers
108 views

Deep meaning of work integral formula [duplicate]

I want to understand very deeply the meaning of the work integral formula: $$ \int m\frac{d\bar{v}}{dt}d\bar{l} \, .$$ It is not enough for me to know that it was defined in this way, I want to know ...
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5answers
118 views

Concept Definitions In Physics eg. $W=\int \vec{F}\cdot d\vec{x}$

What does it actually mean "this concept is defined as ..."? for example when someone tells me "Work is defined as $W=\int \vec{F}\cdot d\vec{x}$". What I understand: I understand the need for the ...
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3answers
147 views

Ultimate meaning of Work

A few days ago I started studying classical mechanics and today I'm stuck with the integral formula for work. I didn't take the formula for granted and i tried to understand it, however, the presence ...
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1answer
24 views

Is there a reference frame in which the static friction from rolling does positive work?

I am worried this will be deleted as a duplicate question, so I will try to be extra clear what I am asking: In some reference frames, static friction can do positive work. If you have a crate in the ...
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1answer
50 views

Energy transfer and Negative work

Is energy always transferred from the source to the object when positive work is done by the source on the object ? If so, what energy is transferred from the earth to a freely falling body ? The ...
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3answers
91 views

Thermodynamics : Pressure of a gas

While reading The kinetic Theory of gases in Feynman Lectures , i was hoping for an explanation concerning the factor (2) that shows that only half of the atoms are headed towards a piston, while the ...
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1answer
53 views

Net work done in lifting

(g is assumed as 10 $ms^{-2}$) We lift a stationary object of mass, $m$, to a height $s$, ensuring it has got a resultant upward acceleration of 2 $ms^{-2}$. The required force to be applied by us ...
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1answer
42 views

Work from string wrapped around cylinder [closed]

A cylinder, on a level surface angularly accelerates as a string wrapped around is put under tension. Because this string causes the cylinder to roll without slipping, the tension force cannot to any ...
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2answers
53 views

Why is there no negative sign in the formula of work against electric field?

Why is there no negative sign in the first formula of work done against electric field where as second formula below has it?
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4answers
72 views

Mechanical Energy Concept Problem

When an object is at rest on a smooth horizontal "surface" (floor) its potential energy $P_E$ equals zero and, as the object is at rest, its kinetic energy $K_E$ is also zero. When the same object is ...
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2answers
53 views

The formula of voltage

Definition from Wikipedia: An electric potential (also called the electric field potential, potential drop or the electrostatic potential) is the amount of work needed to move a unit of positive ...
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2answers
67 views

Expansion of an ideal gas at constant pressure

I approach these expansion problems like so: The gas and the surroundings(piston+outside) are at the same pressure at first. We heat the gas. The pressure rises inside the syringe a bit. The gas ...
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1answer
39 views

How do electrons gain energy in a cell?

When electrons reach the positive terminal, how does the cell do work on them? I’ve read in a book that states voltage is literally the push that the cell exerts on electrons, which thus does work on ...
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2answers
63 views

Moving a charge and potential energy

When talking about bringing a charge from a reference point to another point, we consider the work done by an "operator" force opposite to the electric one, but wouldn't that just cancel the ...
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3answers
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Is there a relation between work and energy?

I am in high school, and I know that work=forcedistancecos and i also know KE=0.5mv^2 and that PE=mgh and that ME=PE+KE , but my question is if there is a relation between work and mechanical energy(...
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Why there is $1/2$ in $KE=(1/2)mv^2$ and Etc [duplicate]

Hello I’m a high school student, my teacher asked the class for why and how there is a 1/2 in (KE=1/2mv^2)&(PE=1/2 k Δx^2)&(PE=1/2 c(Δv)^2)&(KE=1/2 I W). This is my first time on this ...
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1answer
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Object System and Potential Energy [closed]

I know that the object system doesn't incorporate PE due to gravity, but does the object system usually include PE due to springs or other factors, or is the object system exclude all PE and you would ...
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2answers
65 views

Does the work-energy theorem assume that the particles of the system have time-independent masses?

$\newcommand{\force}{\mathbf{F}}$ $\newcommand{\velocity}{\mathbf{v}}$ $\newcommand{\position}{\mathbf{r}}$ Here's an incomplete proof of the work-energy theorem: $$W = \int_1^2\force \cdot d\...
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2answers
71 views

Where does the energy for osmosis come from? [duplicate]

A thought experiment: A U-shaped tube with semi-permeable membrane at the base. The tube is completely thermally isolated from its surroundings. The liquid (solvent) is at some temperature $T$. ...
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4answers
131 views

Why do physicists take the convention that a force field is the negative gradient of a scalar field?

A conservative force is naturally the vector gradient of a given scalar field . I don't know why the convention to put the negative sign in front of the gradient operator. Or is this just a ...
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1answer
48 views

Sign of the work done by dissipation forces

I don't understand this passage from the book I'm reading: Physically, it is clear that a system cannot be conservative if friction or other dissipation forces are present, because $\mathbf{F}\...
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0answers
65 views

What is the formal definition of energy in physics? [duplicate]

What is the formal definition of energy in physics? My question is what is the definition of energy in physics in general ? Moreover is energy a naturally occurring quantity or is a term defined in ...
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2answers
65 views

Work kinetic energy theorem

I don't understand the wordings of this theorem. Can someone please help me in understanding this? Secondly on what basis are the sign conventions in this theorem applied? I get confused in plus and ...
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4answers
70 views

Potential Energy in conservation of energy [closed]

In energy conservation theorem, everywhere $PE=mgh$ is used. What I found is that change in PE= mgh. According to me, while calculating total energy, instead of change in PE, total PE should be used ...
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Is the work-energy theorem only valid for conservative forces? [duplicate]

I have learnt that it states "The work done on a body is equal to the change in kinetic energy of the body" which we derived by considering a position-dependent force. However, if mechanical energy is ...
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Work of van der Waals gas in a isotherm expressed with respect to the initial and final pressure and temperature

The work of a van der Waals gas during an isothermal transformation is readily found to be ($n=1$ mol) \begin{equation} W =RT \ln\frac{V_1-b}{V_2-b}+a\left(\frac{1}{V_1}-\frac{1}{V_2}\right)\qquad (...