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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Is the definition of work related to the nature of the fundamental interactions?

I am having troubles trying to understand why is work defined as it is. So, I know how work is defined: $W = \vec{F}\cdot{}\vec{d}$ (F is the force, d the displacement) and I am okay with it. This, ...
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Non-Work energy conversion

Are there any conversions of energy that are not considered work, (energy change with a force and displacement)? For example heat transfer does not convert the form of energy, can something such as ...
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What is the work done by friction on a body from the perspective of different observers using the formula $-μmgl$?

Consider two observers moving with respect to each other at a speed $v$ along a straight line. They observe a block of mass $m$ moving a distance $l$ on a rough surface. The change in KE of the block ...
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Concept of work [closed]

How was the concept of work and energy invented in physics? What is the actual idea behind work and energy? Why are distance and force specifically used to define work, why not time instead of ...
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The work done by tension and normal forces are conservative or non-conservative? Give reasons [duplicate]

The work done by tension and normal forces are conservative or non-conservative? Tension as well as normal forces does work but has no field. Simultaneously their work is not always path dependent. ...
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General treatment of surface tension non-relativistic classical theory

I'm reading lecture notes on fluid mechanics course, and I wrote that an algebraic definition of surface tension can be constructed from work per unit area to balance the forces along the surface. ...
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Mechanics | Use the work-energy principle to find the speed of the book as it hits the floor [closed]

Problem A small book of mass $m$ is held on a rough straight desk lid which is inclined at an angle $\alpha$ to the horizontal, where $\tan\alpha=\frac34$. The book is released from rest at a distance ...
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Question regarding kinetic energy of a body

Suppose you pushed a block very hard for a small interval of time. Then it traveled some distance 'S' and stops due to friction. You haven't applied force upto the 'S' distance. The force applied by ...
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Question regarding kinetic energy and final velocity of the body

Suppose there is block of mass 'M' kg . You applied the force of 'F'N on it , as a result it get accelerated. Then it acquired final velocity 'v'. The kinetic energy of the block is 1/2(MV²). My ...
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Velocity- and time-dependent forces can not be conservative [duplicate]

I have already seen many posts about this specific question but in only a few of those mathematically rigorous answers were given. Unfortunately none of them are accessible at my level (first year ...
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In an isothermal process there is no change in internal energy, but why in an isobaric one?

In an isothermal process, the heat Q added (which increases the temperature and internal energy) is exactly cancelled out by the work W done by the gas in the environment (which lowers the temperature ...
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Work done by battery [closed]

In charging a capacitor to a charge $Q$ Is there an equivalent to this in setting up current through an inductive circuit? Energy stored in inductor $= 1/2Li^2$ What would be the work done in setting ...
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Why is the friction in the motor wrong as an answer to wasted energy in this question?

I do not understand why the answer to part b)ii) cannot be energy lost to friction within the motor as the work done by the motor should be the total work done to move the cyclist and should include a ...
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Enthalpy, why is work only partially done?

If a system with const. pressure can change it's volume free, a heat transfer into the System results in a partial work done, which gives back the inner energy addet partial back to the environment. (...
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A ball of mass 22g moves to the left at a speed of 35 m / s [closed]

A ball of mass 22g moves to the left at a speed of 35 m / s. How much work needs to be done on the ball to start moving to the right at a speed of 35 m / s. When considering ignore any energy losses
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What is the source of isothermal work?

The usual explanation of isothermal work, especially in the context of the Carnot cycle, is that the "heat" absorbed in the isothermal leg is converted into "work" done on the ...
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Conservation of energy and work done by a torque [duplicate]

Suppose you let a solid roll down an incline without slipping, from height $h$. My textbook gives the following conservation of energy relation $$mgh = \frac{1}{2}mv_{cm}^2 + \frac{1}{2}I\omega^2.$$ ...
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Does the kinetic energy theorem imply that any body on wich is exerted the same space-dependent force is equally accelerated?

So, we have a body $P_1$ of mass $m$ that travels from $A$ to $B$ along a straight line, on wich is exerted a constant force $F$ dependent only on the position of $P_1$. We know that the work done is $...
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Work and Dielectric Shell

Consider a dielectric shell with inner radius R1 and outer radius R2, if I were to carry a point charge q from infinity to the center of the shell, what is the total work done by me? This is the ...
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Is work done by torque due to friction in pure rolling?

This question has been asked and answered numerous times. I went through almost all of them and found no consensus. I found that all of the answers can be divided into two categories: Friction does ...
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What exactly is the limiting factor of the efficiency of a heat engine?

In an imagined scenario, $n$ moles of steam at a temperature $T_h$ and pressure $p$ enter an engine. The steam leaving the engine is at a temperature $T_c$ and pressure $p$. In this scenario, the heat ...
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When using pressure energy to state Bernoulli's Theorem, why do we say it's simply pressure?

I was asked this question in my viva and I couldn't answer. I know there's the whole mathematical explaination of this, when we multiply Force/Area with displacement and convert it into Energy/Volume, ...
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Are there two work-energy theorems (rotational and translational) or just a single theorem for both?

Suppose a body is able to rotate. If work is applied to it along a path $C$, the traditional work-kinetic energy theorem states that $$W_{\mathrm{translational}} = \int_{C} \vec{F} \cdot d\vec{r} = \...
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Centripetal Force question

Since no work is done in circular motion due to no change in kinetic energy (constant speed) and force being 90 degrees from displacement(centripetal force). Does that mean changing an object's ...
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Is there a formula of heat that expresses it in microscopic work done?

If I understand correctly looking at the first law of thermodynamics we have a microscopic work term (heat: $Q$) and macroscopic work term ($W$) $$ \Delta E = \Delta Q + \Delta W$$ The macroscopic ...
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Is energy infinite in an electric field?

Energy is defined as the capacity to do work. Work in turn is defined as force x displacement. An electric field exerts the field in all directions infinitely (even though the strength of that force ...
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How to justify that Carnot loop for ideal gas is closed on two sides by adiabatic curves?

I'm trying to figure out how to show that the orange curves connecting the two green curves are infact adiabatic: The set up is that I have an ideal gas, and I am searching for the loop when it's ...
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Understanding the shape of Carnot loop in the $p$-$V$ plane

The area enclosed by a loop is the total work done. If you draw a square, isn't that the maximum amount of work done possible instead. Why is the isothermal/adiabatic path the most efficient instead ...
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Relation between Work-Energy Theorem and Collisions [closed]

I am stuck on this idea relating the Work-Energy theorem and collisions. The derivation for the Work-Energy theorem is entirely mathematical, and simply involves Net work on a system = $$W_{net} = \...
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Confusion with Gibb's energy [duplicate]

For a reversible process , I can show that $$\mathrm dG=0$$ For the same reversible process I can also prove that $$\mathrm dG=\mathrm dW_{\text{max, non } P-V\text{ work}}$$ Does that imply maximum ...
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Work done on a probe

When moving a probe from the radius of a planet to a new orbit of radius 2R, do we find the work done by subtracting the final potential energy from the initial potential energy? That would give GMm/...
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Can we define $\text dW$? [duplicate]

I am currently taking applied thermodynamics at my university, and for the definition of entropy this is the formula used in the book (Thermodynamic for Engineers by Moran, Shapiro, Boettner, Bailey): ...
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This question is about motor power requirements

If I have a motor that has a power of 20 kilowatts, does that mean that the motor can produce a torque of 10k newtonmeters at 2 rpm, or analogously a torque of 2 newtonmeters at 10k rpm since the ...
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Why is Power = Voltage $\times$ Current?

So P = I*V because V is the amount of energy per coulomb and I is the amount of electrons going past a cross sectional area in one second. So if we do the math, since V = J/C and I = C/sec, if we ...
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How inexact differential shows work is a path function

While my professor defining the work , he says the work is the taken as inexact differential and also says this shows that work is path dependent function but there was no reasoning how inexact ...
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In work done, more force should be applied (to move the body) than is being applied (currently) on the body, while moving the body against field

We define work done as force applied multiplied by displacement. Let's say a field applies a force $F_1$ on a body $b$. Let the distance between point $A$ and point $B$ be $d$ Then work done in moving ...
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How to justify Mechanical Works doesn't involve heat variations?

My professor while teaching Mechanical energy said all the mechanical works are performed at at a constant temperature and said this is the main difference between the thermodynamic work and ...
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A block starts from rest at the top frictionless slide at a height $h_1$ above the ground and leaves the slide perfectly horizontally

A block starts from rest at the top of a frictionless slide at a height h1 above the ground. The block leaves the side moving perfectly horizontally at a height h2 above the ground. The block ...
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Newton's Third Law and Work Done on a Body [duplicate]

Say I push a box with a constant force $F$ causing a displacement $d$. So magnitude of work done by me on the box is $W=Fd$, and the kinetic energy gained by the box is $W$. But according to N3L, the ...
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Work done in inducing emf across moving rod

I saw a proof of the induced emf of a rod/wire moving perpendicular to a uniform magnetic field. My problem comes with the first step of the proof. Proof Suppose we have a wire of length $l$. Consider ...
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Why gravitational potential away from a planet increases?

textbooks---- "potential increases towards infinity and is maximum at infinity" But that is true only when we are seeing potential w.r.t Earth EXPLANATION--------- So , as we know that ...
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Path dependence of non-conservative forces

In almost every place the statement regarding non-conservative forces is: In the case of non-conservative forces, the work done is dependent on path taken between two fixed points. Longer the path, ...
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Find the work to move a coil in an uniform magnetic field [closed]

we have a rectangular coil ($d$ and $3d$ wide) in a magnetic field as in the picture. To the left we have $B_0 T$ and to the right $\frac{B_0}{2} T$. There is a counterclockwise current in the coil ...
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Question regarding Conservative Forces

Work-Energy Theorem States that $dT=F.dr$. On integration we can see that $T_2 - T_1$ = $\int_C F.dr$ (C is the curve along which the object moves) Does this mean the force can be expressed as $\...
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Change in gravitational potential energy when the work is zero

I may be misunderstanding the whole concept , but my doubt is this. Let us say there is an isolated system comprising of a rock and the Earth. If I was to lift the rock up with a force equal to the ...
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What is the meaning of external work in electric potential?

We learned that $$-Work = \Delta U = q(Va-Vb).$$ However, we write that $$W = q(Va-Vb)$$ in this question. Why don't we write the minus sign in the equation? How does external work affect the minus ...
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Different result when deriving electric force as $dW/dr$ and $-dU/dr$

Work done by electric field, $W$ is the negative of the change in electric potential energy, $U_r$. $$W=-\Delta U$$ By considering an infinitesimal change in EPE, we can deduce that electric force, $...
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What is the difference between kinetic friction and internal kinetic friction?

I came across the following question in my homework assignment: Which of the following statements is TRUE for a system comprising of two bodies in contact exerting frictional force on each other : (A) ...
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When are pseudo forces considered to do work?

I was solving a question in which: there is an inclined wedge with a smaller block on the inclined side of it (all surfaces are smooth). The wedge is then given an acceleration by application of an ...
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Formula for work done for both conservative and non-conservative force are different?

We know that the formula for Work Done by an constant force is W.D = Force x displacement x (cosine of angle between force and displacement). Situation: A mass m travels 10 meters towards  +ve axis ...
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