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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Work-Energy Theorem

Regarding the function theorem: W (non-conservative force) = △ K, this formula I once derived, it is also acceptable, but I saw W = △ K + △ U in the reference book a few days ago, I don't understand ...
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Is this true about potential energy?

Work done by an external force on a system equal and opposite to a conservative force is stored as potential energy within the system. We choose an arbitrary location x and define the potential ...
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Conservation of momentum and work

Consider the following scenario: I am alone in space with a ball. I threw the ball at a certain speed such that i am propelled backwards (like a rocket is) as to conserve momentum. Now, since my ...
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Maximum force on a spring [closed]

Work $W$ is done to extend a spring beyond its natural length by a small distance $x$. Assuming a spring constant of $1$, what is the magnitude of the maximum force done by the person stretching the ...
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Separating a charged capacitor plates connected to a battery [closed]

I have to find work done by external agent against electric force in separating parallel capacitor plates when attached with battery (assuming they have charge Q, distance d¹, and area A kept in ...
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What is the difference between the principle of virtual work and the principle of virtual displacement?

When I read Reddy's book, "Energy Principles and Variational Methods in Applied Mechanics", Chapter 5.1. I am confused with the two jargons "the principle of virtual displacement" and "the principle ...
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How can I see that newton-meters are equal to coulomb-volts?

I know $\mathrm{J} = \mathrm{N\ m} = \mathrm{C\ V}$, but what if I want joules expressed in SI base units of $\mathrm{kg}$, $\mathrm{m}$, and $\mathrm{s}$? This is trivially easy if I use $\mathrm{N\ ...
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What is the heat needed for an isothermal expansion of gas and why do physics and chemistry yield different answers?

One mole of a certain ideal gas is contained under a weightless piston of a vertical cylinder at a temperature $T$. The face of the piston opens into the atmosphere. What is the heat supplied in the ...
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A $2100$kg is travelling at $100$km/h, how would you calculate the minimum stopping distance? [closed]

I used $E=\frac{1}{2}mv^2$ to get its initial kinetic energy: $58,380$ J, in hopes I could use $W = F \times d$ to work backwards and find $d$, but it's not working out. Any and all help is great! It'...
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Work done by Tension on a system-generalisation

In All the Classical Mechanics problems I have come across so far, There's one thing that happens invariably: That the work done by tension is zero. Mostly, It simply happens because the (massless) ...
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Irreversible compression [duplicate]

A vertical thermally insulated cylinder of volume $V$ contains $n$ moles of an ideal monoatomic gas under a weightless piston. A load of weight $W$ is placed on the piston as a result of which the ...
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Work done by action-reaction pair of tension

Work done by action-reaction pair of tension force on a system is zero if the string is inextensible I am trying to understand this statement taking the following arrangement in consideration. Here, ...
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Shoud the total energy of a particle increase when work is done on that particle?

Shoud the total energy of a particle$($kinetic energy $+$ potential energy$)$ increase when positive work is done on that particle? If the answer is yes, then why the total energy does not increase ...
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Work done in rotating a dipole in NON uniform electric field [duplicate]

I understand that the torque on a dipole due to a non uniform electric field is given by the same expression as that of in a uniform electric field i.e. pEsinθ. Now,how do you calculate the work done ...
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When air is pushed into a soap bubble, where does the work go? [closed]

In this problem: Air is pushed into a soap bubble of radius $r$ to double its radius if surface tension is $T$ then whats the work done in the process? I can find out the answer $(24\pi r^2 T)$ by ...
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Is the average force calculated from $F(x)$ the same as that calculated from $F(t)$?

Say a force is doing work on an object in one dimension. I could calculate the average force over the distance with $$\frac{1}{\Delta{x}}\int_{x_1}^{x_2} F(x) \text dx$$ If I also formulated force ...
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In electric potential energy why do we still integrate from infinity to the current distance in the case of opposite charges?

My understanding of potential energy is that it is the work that is going to be done to a particle when that particle is released, in the case of gravity if we release an object it is going to fall to ...
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Thermodynamics First Law: Where is my reasoning wrong?

The first law is given by: $$ \Delta U = Q + W $$ Because of the conservation of energy, we also have: $$ \Delta U_{universe} = \Delta U_{system} + \Delta U_{surroundings} = 0 $$ This implies ...
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Why Force is considered in case of Work done by two bodies? [closed]

Suppose there are two bodies having same mass which are being moved by the same displacement with different Forces. According to the formula: $$W=Fd$$ The work done by the body which applied more ...
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Does a fan rotating with a uniform angular velocity consume electrical energy?

Work done on a rotating body is equal to the change in its kinetic energy. When an electric fan rotates with a constant angular velocity, then its kinetic energy doesn't change. Does it mean that it ...
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Linear relationship between air resistance and power consumption?

Suppose that the air resistance a car encounters is independent of its speed. When the car travels at $15\mathrm{~m/s}$, its engine delivers $20\mathrm{~hp}$ to its wheels. (a) What is the power ...
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Work done by a spring on a block

A spring has a block attached to one end and the other end is attached to a wall. As the ball is displaced right or left, we know spring force $F_{sp}$ $=$ $-kx$, always in the direction opposite to ...
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Work done by elastic force

I have a doubt about the work done by elastic force. The general formula of the work is: $W_{Fe} = \frac{1}{2}k(x_0^2-x^2)$; if we take that the state in which the spring is at rest, we have: $W_{Fe} ...
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Why does less force correspond to less work done?

I'm confused with the definition of work in physics. I know that it's defined as a product of force, displacement and a cosine of angle between them: $W = F s \cos(\alpha)$. But that means that the ...
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What's the difference between the work done by a force and a couple with constant moment of inertia?

The work done by a force in case of rotation is : $$W=F.\overset{ \huge\frown}{AB}=\mathscr{M}\Delta \theta$$ Of course if we considered that the body is translated from $A$ to $B$ with an angle $\...
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Work and Electric Potential Energy

A positive charge will move from high potential to low potential, meaning that it will lose electric potential energy. If that is true, how is the work done by the E-Field on this positive charge?
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Work done by electric force when moving like charges together

Consider two positive charges. I would like to find the work done by the electric force on charge +q as it is brought closer to charge +Q from radius a to b. I first define electric force as a ...
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$W_{total}=W_{external}+W_{by, gas}=0?$

Consider pushing a closed piston filled with air inwards with an external force which exerts a pressure of magnitude $p$ onto the syringe. If we know that $$\delta W_{EXT}=-p dV$$ and by definition $$...
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Minimizing a Line Integral of a Vector Field Using Euler-Lagrange---Problem with Boundary Conditions

Let $F:\mathbb{R}^2\rightarrow\mathbb{R}^2$ be the following vector field: $$F(x,y)=\left< x\cdot p(x,y(x)), y(x)\cdot p(x,y(x))\right>$$ where $$p(x,y(x)) = \frac{5x}{6} + \frac{7 x^2}{4} + \...
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Is this an acceptable use of $a \,dx = v \,dv$? [closed]

From the chain rule we have $$a\, dx = \frac{dv}{dt}\, dx = dv\frac{dx}{dt} = v \,dv$$ This was introduced in an early chapter of my physics textbook and I have been getting a lot of mileage out of ...
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Is 1 Joule the work done to lift ~100g through a distance of 1m? [duplicate]

I am seeing many videos saying that 1 Joule is the work done to lift ~100g through a distance of 1m (like this one https://youtu.be/BYpZSdSEk4A?t=348). The idea is that 100g has a gravitational force ...
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Minimum work on a plane [closed]

Consider a block placed on a rough horizontal surface where the frictional coefficient between the surface and the block is $\mu$. Suppose I need to find the minimum force that must be exerted to make ...
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Spring whose spring constant is a piecewise function of displacement—is this possible?

A bungee cord is essentially a very long rubber band that can stretch up to four times its unstretched length. However, its spring constant varies over its stretch [see Menz, P.G. “The Physics of ...
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How much work is done by bringing two positively charged rods together? [closed]

We have two positively charged rods placed far apart. First rod has a charge $e_1$ and length $L_1$, second has a charge $e_2$ and length $L_2$. How much work is done, when we push them closer to a ...
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Why we don't work physically when we don't make something move? [duplicate]

The formula for Work is F*x, where x is distance taken. So by physicially work formula, why don't we experience any work if we do not make any object move? Is there a specific reason? Example, I am ...
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How can kinetic energy not be conserved if momentum is conserved in a system? [closed]

If there is no net force on a system, energy is conserved. Then, how can there be work at all since work is the integral of dot product of force and $dr$ ? If force is $0$, wouldn't work ...
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If application of force does not result in spatial movement, has work been done? [duplicate]

I'm trying to help my kids why their elementary-school physics. Their lesson today says that "work" is done only when a change in position is accomplished by the applied force. I have absolutely no ...
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Missing force in the system

What exactly is the cause/source of the energy loss in a non-elastic collision? The forces during a collision are the Normal forces: which don't do work I believe. The Discussion with FakeMod ...
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What is wrong with this calculation of work done by an agent bringing a unit mass from infinity into a gravitational field? [duplicate]

Let us assume that a gravitational field is created by a mass $M$. An agent is bringing a unit mass from $\infty$ to distance $r < \infty$, both measured from mass $M$. The agent is always forcing ...
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Why isn’t there a $\cos(\theta)$ in the work-energy theorem? [duplicate]

please don’t use any calculus in your answers I was reading the derivation of the work energy theorem in my textbook and it goes like this: $$W = Fs\Rightarrow W_{net} = mas$$ Since $v^2 - u^2 = 2as ...
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Why is the gravitational potential energy defined as negative? [duplicate]

It is said that since work is done by the gravitational potential itself , so at a finite distance the gravitational potential energy of the body is negative. Could someone explain why?
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Can we apply work energy theorem in non-inertial frame of reference? [duplicate]

Can we apply work energy theorem in non-inertial frame of reference? I am totally confused in this matter due to the work of pseudo force.
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Thermal Energy, Heat and Friction using work-energy [closed]

The work-energy theory states: $\Delta$ K = W John Taylor breaks work into conservative and non-conservative work: $\Delta K = W_c + W_{nc} $ One type of non-conservative work is friction, ...
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Work done to slide a circle over another circle assuming a horizontal force and no friction

There are two ways that I think that this problem may be able to be solved, however, they give different answers, therefore at least one of them is incorrect. Let's start with a simpler problem, the ...
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Enthalpy change in irreversible adiabatic isobaric process

In an irreversible adiabatic isobaric process why is the enthalpy change given as $\Delta H<0$. Any help is appreciated.
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How can I find the minimal work that can act on an object being pushed up a flight of stairs?

The question I have is that the object is being pushed up a flight of stairs (inclined at 42°) and I have to find the minimal work possible that can act on the object. I think it should be 0 joules ...
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Is work-energy theorem valid for Power = force * velocity?

Work energy theorem states "work is said to be done when there is change in Kinetic energy", i.e. $W = ∆KE$ but as we know, $P=\vec F \cdot \vec v$, where a constant force $\vec F$ maintains a ...
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Why doesn't the work done by atmosphere contribute to increase in internal energy of gas?

Say that I have a vertical thermally insulated cylinder which contains an ideal monoatomic gas under a weightless piston and the system is initially in equilibrium. Now if a load of weight $W$ is ...
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Is energy needed to release or absorb energy?

Is energy itself needed to release or absorb energy? Or do all bodies have energy already to do work due to their mass ? Can light energy for eg. “absorb” more energy? For energy to be absorbed or ...
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When the derivative of potential energy is equal to zero why are the net forces zero?

Well, as far as I have been taught and know :$$\vec F = -dU/dx $$ But then my teacher also told me that when the derivative of potential energy is zero the $"net"$ Forces are zero. But this ...

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