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

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55 views

Newton's third law of motion versus Work

Newton third law of motion says that "To every action, there is always an equal and opposite reaction". The vector study tells us that if two vectors are of same nature and equal magnitude but ...
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42 views

Does $\delta W=pdV$ hold for non-ideal gases

I have that for quasistatic processes, $$ \delta W= \textbf{f}\cdot d\textbf{x} $$ so for a gas $\delta W=pdV$. Does this only hold ideal gases or will it hold for van der waal's gas?
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803 views

Work done against gravity [closed]

The work done against gravity is $mgh$, well at least that's what my textbook says. I have a question: I can apply a force say 50N, so total work done = $mgh + mah$. Where $ma$ = Force. But the truth ...
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89 views

Energy density and Carnot cycle

For example, diesel has about 40 MJ/kg, what does it mean? Is that if we burn it we will get 40 MJ of energy per kg, but we can not get all of it to mechanical work? If that is the case, then why ...
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126 views

Confusion with curl of Lorentz magnetic force

Since the magnetic force is a no work force, $dW=\vec F\cdot d\vec r=0$ for $\vec F(\vec r)=q(\vec v(\vec r) \times \vec B(\vec r))$, therefore $\oint \vec F \cdot d\vec r=0$ by Stoke's theorem. ...
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118 views

Work producing current = energy stored in the magnetic field?

It is stated that "the formula for the energy stored in the magnetic field is: $$E = \left(\frac{1}{2}\right)(LI)^2$$ and the energy stored in the magnetic field is equal to the work done to produce ...
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289 views

Measuring energy when no work is done — comparing push-ups to planks

tl;dr Is there any meaningful (physical) way to compare the energy expended in the exercise of doing $x$ pushups in $t_1$ seconds, vs the exercise of doing the plank for $t_2$ seconds? I'm ...
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650 views

Why the electric force does no work on the charge when perpendicular to the field?

I was reading my physics textbook and came across this sentence: When a charge moves in an electric field, unless its displacement is always perpendicular to the field, the electric force does ...
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259 views

A question from a Physics 2 exam: About electron cloud an a constant external field:

I am trying to prepare for my exam in Physics $2$, the following is a question from an old exam (the question also have a detailed answer to it, but I don't really understand it). An acceptable ...
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274 views

Why work to change velocity from 0 to 20 km/h is less then from 20 to 40? [duplicate]

Imagine spaceship in vacuum with mass = 1. At beginning, it has velocity 0, and kinetic energy 0. $$W_1 = 0$$ Then, it turns on its engine, and changes velocity from 0 to 20 (delta v = 20). It's ...
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229 views

How can I understand work conceptually?

I'm in a mechanical physics class, and I'm having a hard time understanding what the quantity of work represents. How can I understand it conceptually?
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2k views

Work done in projectile motion

A projectile is shot at some inclination to the ground. It falls at another point having R distance from the initial point on the ground. Is there any work done? If initial velocity vector is $(u\cos ...
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1k views

Why is work defined as force dot displacement?

Why is work defined as force dot displacement? I know that it is defined like that based on the observational fact - we do more work when we apply greater force or move to a greater distance. But I ...
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4answers
6k views

What is the electric potential at a point?

1) What does the electric potential at a point exactly mean? My teacher tells me that current flows from higher potential to lower potential but when I ask him the reason, he fails to give me a ...
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46 views

Why am I getting that work it's always the same in both directions?

I'm studying electrostatic and I'm getting pretty frustrated because with the definition of work I'm getting that it's always positive and it doesn't make any sense. So here I have 2 positive ...
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31 views

Do transferring energy and applying force to a body imply same?

Do transferring energy and applying force to a body imply same meaning? When we say, "I throw a ball using my pushing force so on the other hand, can I say that I transferred my kinetic energy to the ...
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3answers
88 views

A problem related to Work done by falling bodies : Expert's attention much needed! [closed]

I'm having a lot of trouble with this question, that I've found in my textbook. I've solved it in my own way and it's very simple! But the solution in the book is totally different. It doesn't make ...
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1answer
64 views

How can a magnetic field produce an emf if the force produced does no work?

In the textbook I'm reading it gives an example of where a person pulls a rectangular wire with a velocity $v$ and the left side of that wire is in a uniform magnetic field. After some ...
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81 views

Can magnetic force do work? [duplicate]

I have been told numerous times that magnetic force do no work at all but I have some trouble digesting this fact. Now suppose we have two straight wire with some current, they certainly can feel ...
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61 views

Line integral calculates work, even though the force from the vector field doesn't cause the movement?

I'm afraid the title here was unclear, so I'll attempt to make things a bit more clear. I am conceptually confused about the physical meaning of line integrals over a vector field, so I'll pick an ...
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71 views

Confusion with Grounded Conductor: bringing in a point from infinity

Suppose, for sake of argument, we have a spherical grounded conductor at the origin. Additionally, let our reference voltage be at infinity. Now, I view the potential of a point in space as being the ...
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3answers
351 views

Why does the work done by an internal force differ from the work done by external force?

Let's consider the following situation. We put a body of mass $m$ at a distance $A$ from the center of Earth. We let the Earth attract the body and analyze the situation at a point $B$, closer to the ...
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126 views

Work done by gravity on a ball & the ball on earth

I have studied today that if a ball was to fall a certain height, then the work done by gravity on the ball would equal the work done by the ball's equal and opposite gravitational pull. By $W=Fd$, ...
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56 views

Action Reaction Pairs and Work

Say that a ball is sitting in front of a compressed spring launcher. The spring is then released. The spring applies a force on the ball for a certain distance. This force is accompanied by an equal ...
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86 views

Placing two similarly charged particles in space

Now, I will make a hypothetical situation. Assume that we place two similarly charged particles (lets take electrons) in space. Imagine that there is no other force acting on the particles except the ...
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117 views

Exertion from swinging on a playground swing

I've read about how by tilting one's body one changes one's center of mass while swinging on a playground swing, and thereby increases the energy of the swing. But I would like to get a better sense ...
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433 views

Work on Ferromagnetic Object Due to Solenoid

I've been going through some equations and such trying to determine the work done by a solenoid on a ferromagnetic object. I have the following: Magnetic field due to solenoid: $\vec{B} = ...
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2k views

How is it possible to equate the internal energy at constant volume with the internal energy of an adiabatic process?

I hope my question makes sense. My problem is that, I have read through numerous textbooks that $$nCdT = -PdV$$ (where $NC$ is constant volume) when deriving the relationship between $T$ and $V$ for ...
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307 views

calculating work done by friction

I want to calculate the work done by friction if the length $L$ of uniform rope on the table slides off. There is friction between the cord and the table with coefficient of kinetic friction $\mu_k$. ...
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798 views

Mechanics Question: Energy, Work and Power

I'm a pure mathematician by trade, and have been trying to teach myself A-level mechanics. (This is not homework, it is purely self-study.) I've been working through the exercises and have come up ...
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1k views

Calculating force required to stop bungee jumper

Given that: bungee jumper weighs 700N jumps off from a height of 36m needs to stop safely at 32m (4m above ground) unstretched length of bungee cord is 25m Whats the force required to stop the ...
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135 views

Carrying water on person, or on the frame when bicycling

So, the question is as follows: What is the difference in work exerted by the rider in the two following scenarios? a) Rider + bike. Water carried in a holder on the frame b) Rider + bike. Water ...
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1k views

Statics software for structural engineering [closed]

I'm attempting to expand my knowledge of engineering software. I've found comsol and ansys for acoustics and thermodynamics/fluid dynamics (not necessarily in that order), now I'd like to see if I can ...
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26 views

How much power does it take to keep a massive particle suspended in a gravitational field?

For instance if I have a rocket of mass $m$ in a uniform gravitational field $g$, and I want to keep it floating in the air via thrust alone, then how much power in the form of (say) chemical energy ...
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45 views

Who is said to do Work, me or the body?

If I subject my force to a body and it is displaced then the work is said to be done. What is that work done by? Is it said to be done by me or that body?
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25 views

Issue with Work-Change in KE equivalence

First-year physics student, with a pretty basic question. I've seen proofs that Work = Change in Kinetic Energy involving calculus, and they make sense to me, but I'm not sure why the following, much ...
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47 views

Necessity of the Notion of Work and Kinetic Energy

I've worked through many example problems in my college physics text in the section on kinetic energy and work. I noticed that if the desired quantity is velocity or force, they can be solved entirely ...
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95 views

Is the work-energy theorem valid for only particles or rigid bodies as well?

Is the work-energy theorem valid for only particles or rigid bodies as well? Most places where I have read this seem to claim the latter. But an example I thought up has been troubling me. Consider ...
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52 views

What is in the gravitational field that is making the work done independent of path taken?

I could not understand the same path independence in electric field. So I am trying to understand it first in gravitational field and then apply it to electric field.
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27 views

Work done by a homogeneous gravitational field on a system of particles

Perhaps this is trivial: how does one prove that the work done by a homogeneous gravitational field on a system of particles is equal to the work done on a point mass with the total mass of the ...
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69 views

Work done: kinetic energy or area under F-ds curve?

Starting from $$F=ma = m \frac{dv}{dt} = m \frac{ds}{dt} \frac{dv}{ds} = m v \frac{dv}{ds}, $$ leads to work done = integral of F.ds = integral of mvdv = change in KE. Suppose a variable force is ...
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67 views

Do components of force have direction when doing work?

When we get angle > 0, the x-component of force is along the direction of displacement and so their product is called Work. So the x-component of force is said to have direction of the respective ...
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75 views

What is the work done said when angle between force and displacement>90 and <180?

If the angle between $Force$ and $Displacement$ is obtuse then by using the formula of $Work$ we get negative quantity so is it said then that the system is losing energy or it is merely for the case ...
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80 views

Factors on which Coefficient of restitution depend

What are the factors on which coefficient of restitution depend? What is the reason for more coefficient of restitution of two glass balls (0.95) than for two lead balls (0.20)?
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5answers
716 views

Why is kinetic energy stored as potential energy in a body during its motion against gravity?

Everyone knows kinetic energy is converted to potential energy in the body when it moves up against the earth's opposing gravitational force. But I am facing some problem with this. What I learnt ...
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315 views

Difference between heat and work

According to the Kinetic Theory of Matter, temperature is nothing but a measure of the kinetic energy of matter. My textbook says that the change in internal energy of a system is the heat gained plus ...
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82 views

Where does energy go when performing a useless effort?

I went to school one day, so I thought I was able to get this simple one.. but it looks like I'm not anymore. :( One lonely little spaceship is resting into space. It has a small fuel capacity that ...
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116 views

Does distance traveled by a vehicle after its engine has been switched off depend on its mass at all?

A vehicle moving with some velocity on a rough horizontal road finally comes to rest after its engine has been turned off. Intuitively, it seems a vehicle with greater mass would stop first because it ...
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116 views

Work done in pulling a rope from a boat

A boy sitting on a boat pulls on a rope with a constant force $F$ over a duration of time $t$. The other end of the rope is either tied to a bridge or to another freely floating boat of equal mass. ...
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45 views

Why is work not related to velocity?

A very simple question; why does it cost me more energy to very slowly lift a mass $m$ over my head compared to very fast? The definition of work does not state anything about velocity, only the ...