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 done on a quantum state

I have a Hamiltonian $H _{\lambda(t)}$, where $\lambda(t)$ characterizes a time-dependent path in parameter space. The parameter is changed in finite time from $\lambda(t_i)$ to $\lambda(t_f)$ . At $t=...
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What do the terms “Frame specific work” and “Frame dependent work” mean? [on hold]

I was reading a paper published in A.J.Phy. American Journal of Physics 60, 356 (1992)[All About Work] by A. John Mallinckrodt and Harvey S. Leiff There I found this two terms but when tried to ...
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First law of thermodynamics clarification on internal energy

Starting from the experience of joules we know that the mass before falling has a potential energy $mgH$ where $H$ is height from floor. Once we reach the height $0$ we observe that the kinetic energy ...
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Work done by the drift term of Ornstein–Uhlenbeck process

Consider a particle obeying the Ornstein–Uhlenbeck process: $$ dx_{t}=\theta (\mu -x_{t})\,dt+\sigma \,dW_{t}, $$ where $x_t$ is the position of the particle at time $t$, $W_t$ denotes the Wiener ...
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Work and gravitational potential energy in taking a book in different definition of “system” [on hold]

Can some body calculate the work done by person A in moving the book to height $h$ from ground in following three definitions of the system, where initaiial and final velocities are zero: a) only ...
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Work a medium of energy conversion? [duplicate]

Is work a medium to convert one form of energy to other? i.e. to say without work you can't convert type of energy? Similar type of question pertains to heat.heat is also medium of conversion of ...
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Work Done and Potential Energy in Electrostatics

This is a question from class 12 Physics NCERT Part 1: I am having so much trouble with this, I can't figure out where I'm going wrong. I solved part (a) here: (a) U= -27.2 eV (b) Here, the kinetic ...
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Why heat and work?

In thermodynamics we study energy from a heat and work transfer perspective. Confusion: If we take the example of an electric-engine consuming electric energy, creating a momentum/rotation and "...
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Why are you doing no work when carrying a body through a horizontal distance?

Work done on an object is equal to $$FD\cos(\mathrm{angle}).$$ So, naturally, if you lift a book from the floor on top of the table you do work on it since you are applying a force through a distance....
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Why am I getting a negative sign in this derivation?

I want to derive a formula for calculating the final velocity of an object that falls from rest as it reaches the surface of the Earth. I want to take the change in acceleration into account and hence ...
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On work by a electric field in a electric circuit

If the electric circuit is complete, then one can say that the net average displacement of the electrons is $0$. Then consequently the work done by the electric field is also $0$. So how is energy ...
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Is This force applied considered as Work or Torque ,And how do you calculate it?

When I look at the life of one of the most successful arm wrestlers like (Alexy Voevoda), their training is awesome, I had seen a video of him pulling against 3rd person in arm wrestling. Source:...
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How much kinetic energy does a helicopter use in a hover? [duplicate]

A helicopter just circulates air in a hover and maintains a stable altitude. So, how much energy is used to do this? Using the standard equation $KE = \frac12 mv^2$; then the kinetic energy used would ...
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Work done by charged particles [closed]

A proton is kept at rest. A positively charged particle is released from rest at a distance d in its field. Consider two experiments; one in which the charged particle is also a proton and in another, ...
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Can magnetic field change kinetic energy?

An electron and a proton are moving under the influence of mutual forces. In calculating the change in the kinetic energy of the system during motion, one ignores the magnetic force of one on another. ...
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102 views

Isn't friction on an incline coefficient of friction times the Reactional force?

Question - "As shown in figure a body of mass 1 kg is shifted from A to D on inclined planes by applying a force slowly such that the block is always in contact with the plane surfaces. ...
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Height and Velocity vertically falling body

Feynman wrote in his lecture From Newton’s Second Law we can easily tell how the object moves, and it is easy to find out how the velocity varies with time, namely, that it increases proportionally ...
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What's wrong with this argument that the potential energy of an arbitrarily heavy object at arbitrary height is $0$?

Consider an object with mass such that there is a gravitational force downward of $1N$. Also assume the environment is a perfect vacuum. Now assume that we exert a force of $1+\epsilon $ Newton upward ...
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Physics of Athleticism for Dunks

I was curious of the athleticism I'd need to dunk a standard rim at $10$ ft above the ground. Using an online calculator, given that I am $5$ feet $6$ inches tall with a standing reach of $7$ feet $1$ ...
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Regarding the definition of the electrical potential energy

Let us say we have two charge positive $q_{1}$ and $q_{2}$ very far away from each other. Suppose also that $q_{1}$ is stuck in its place. If we want to bring them closer to some distance $b$ apart, ...
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Why pulley systems give mechanical advantage?

In a system with 2 pulleys, to lift a x kg object y meters I would need half the force that the object exerts due to gravity but pull the rope double the distance, why does this happen this way?
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41 views

Find the work done against the force

If there is a force $\mathbf F(x)=ax\hat i$ and an object is moving from $x_2>0$ to $x_1>0$ in the opposite direction of force. Then work could be calculated as follows $$\int_{x_2}^{x_1} -F(x)\...
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Calculate work done by a hovering helicopter over time

This is likely to be very simple, but... How does one calculate work done by a hovering unmoving aircraft over time? As in work in Joules. In this scenario, to remain hovering the aircraft has to ...
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163 views

Why is carrying a heavy object more taxing on the body than pushing the same object on wheels?

Where is the "extra help" coming from when rolling the object on wheels?
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How to derive $dW = dE$? [closed]

From the definition of power: $$P \ = \ \frac{dW}{dt} \ = \ \frac{dE}{dt}$$ Multiplying both sides by $dt$, we get: $$dW = dE$$ $1.$ What does this imply? $2.$ Are there any other (perhaps more ...
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Is work equal to area between graph and $x$-axis in a graph of force vs displacement?

Is this true even when displacement is not in direction of force? $$W = \int (F\cos\theta)\text dx$$ and area is $\int F \text dx$. In my book that area is given as one of the definitions ...
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How is magnetic energy supplied?

Enthusiastic layperson here, curious about magnetism: Scenario 1: Imagine that I lift a piece of iron with my arm from a tabletop a fixed distance upwards, then place it back on the table. In ...
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Why is there energy being spent / work being done in a static system?

Sorry that I don't have pictures. Imagine I have a steel circle, like a hula hoop. On opposite sides of that circle I attach two springs, then stretch them. They meet in center where I hook them ...
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1answer
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Definition of non-conservative force [duplicate]

In defining conservative force, we say that "The potential energy difference is path independent." However, as far as I understand, potential energy only exists when there is a force field. ...
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Time to move along a path?

Let's say I have an arbitrary path from point $A$ to point $B$. A particle moves from $A$ to $B$ under the influence of gravity but also impeded by a frictional force $\vec{F_\mu}$. The gravitational ...
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Mechanics of a particle problem (potential energy vs. work approach)

I'm trying to reconcile two methods of approaching a problem, see picture below: Disregarding the angle of the surface and any friction, calculate the velocity $v$ of a particle pulled back a ...
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Energy loss caused by a negative work

Let's supposed a box is sliding on a friction-less surface, so it has some KE at this point, and let's imagine an external force is being applied on the opposite direction of the displacement of the ...
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Why doesn't a magnetic field accelerate moving charges?

As a magnetic field of intensity, $\mathbf{B}$ applies a force of $\mathbf{F}= q\mathbf{v} \times \mathbf{B}$ on a charge $q$ moving with velocity $\mathbf{v}$, this force $\mathbf{F}$ should be ...
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Work done over a closed loop

Is it true that the work done in the motion of a body over a closed loop is zero for every force in nature?
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Confused about the differential of a quantity

We know that by definition, the differential of a single variable function $f(x)$ is $$df(x)=\frac{df}{dx}dx$$ analogously, for a multi-variable function $f(x,y,z)$ $$df(x,y,z)=\frac{\partial f}{\...
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How does the battery do work on the electron although the speed of electrons is constant

In a simple circuit how does the battery do work on the electrons of the wire although their speed is constant . Imagine I want to take a body which has 5 Newtons weight from the ground to 10 meters ...
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Conservation of energy with friction on a pool ball

I have a problem where I am given the mass $m$, radius $r$ and friction $\mu$ between a pool ball and table. The ball is not initially moving but at $t=0$ is struck by an impulse $$p=\int_{-\epsilon}^...
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$pV$ work and Specific volume [closed]

I am working on a $pV$ work exercise. I am given $P_1$, $P_2$, and $V_1$; we can solve for $V_2$. I am also given mass. I am told that the $pV$ relationship is $pv^{1.2}=const.$, where $v$ is ...
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Derivation of the K.E. formula without the work-energy theorem (or proof of the work-energy theorem without the kinetic energy formula)

All of the derivations I have seen for the kinetic energy formula have relied on the fact that work is the change in kinetic energy, something like the one found here: How to prove equation of kinetic ...
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37 views

Work done by static friction in Rolling

In rolling without slipping, I understand that the velocity of the point where static friction with the ground is 0, and therefore static friction cannot do work. However, from newtons laws, an object ...
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Does the force of friction helps us to accelerate while running? [closed]

The question is to find the correct statement: Cause of increase in kinetic energy while running is due to the work done by friction force without which he cannot run. OR Cause of increase in kinetic ...
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Can a heat pump have efficiency greater than 100%?

A heat pump has an efficiency greater than 100%. Does this violate the laws of thermodynamics? My answer: I'm assuming that "heat pump" means heat engine. $e>1$ $\displaystyle\implies\frac{W}{...
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How is it possible to have different answer using two different equation for same condition? [closed]

There are two blocks ${(m_1 ,m_2)}$ of different masses placed on a surface, connected with a spring of spring constant $k$. The coefficient of friction between the blocks and surface is $\mu$. Now we ...
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113 views

Is net work always equal to the change in kinetic energy?

I know that $$W_{net}=\Delta K\tag{1}$$ However, I don't know if this is only true in a system where only kinetic energy is present, or if it's also true for a system in which there's potential ...
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Do I do zero net work if I start and stop a spaceship in vacuum?

As question states, I start and then stop a spaceship in vacuum by using orientable thrusters. In the acceleration phase, I am doing positive work, but in the deceleration phase I am doing negative ...
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Can radiation pressure do work, if so does the magnetic field participate?

I understand that the magnetic field cannot do work because the Lorentz force is always perpendicular to the displacement. In my optics book(Hecht Ch3) these equations appear: Electromagnetic ...
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Why a Box moving at Constant Velocity isn't doing Work?

This was a question from an A-Level past paper and the question is pretty straightforward. I was in a hurry so I couldn't think much on this problem and chose $C$ as my answer, checked it on the ...
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103 views

Increase in entropy and integer factorization (How much work does one have to do to revert “irreversible” processes?)

This is not necessarily a direct physics question, but I am hoping, that by posting it here, someone can give a hint from the physics perspective. It is known, albeit not proven, that integer ...
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3answers
213 views

Magnitude of vector quantities

The gravitational force in the vector form is defined as $$ \vec{F}=-\frac{GMm}{\boldsymbol {r^3}}\vec{r}$$ Many textbooks define its magnitude as $$F_g=-\frac{GMm}{r^2}$$ However, in the derivation ...
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Work done by ideal gas under a reversible process which is not isobaric, isochoric, isothermal, adiabatic

First post, sorry for the poor formatting. Question Consider a non adiabatic system closed to mass exchange where an ideal gas traverses along a reversible path from state: to . What is the work ...