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

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Collision of two deformable bodies - limitation of work-energy theorem

I am attempting to model the impact of a deformable body (clean, dry sand characterized as a continuous fluid) with flexible diaphragm (in this case a sheet of rubber). Assuming that this is a closed ...
2
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2answers
362 views

Energy of electron spinning in a magnetic field

When an electron travels in circles in a uniform magnetic field, it must lose energy because all accelerated charges radiate, and must therefore spiral down to the center. Is this energy compensated ...
2
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2answers
457 views

Falling chain with friction

I really need some help with a physics problem, and I guess my doubt is more conceptual, than question based. But still, let me pose it to you: A uniform chain of mass $M$ and length $L$ lies on ...
3
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1answer
344 views

Is my textbook teaching an incorrect concept of Work?

I fear my textbook is teaching an incorrect concept of Work. I am very frustrated right now since I was struggling to understand the concept in the way that was explained in the textbook and my ...
3
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2answers
2k views

work done by tension

The problem statement, all variables and given/known data Consider the following arrangement: Calculate the work done by tension on 2kg block during its motion on circular track from point $A$ to ...
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1answer
662 views

Is there another way to calculate the work done by air resistance?

A ball of mass $0.37\text{ kg}$ is thrown upward along the vertical with a initial speed of $14\text{ m/s}$, and reaches a maximum height of $8.4\text{ m}$. a) What is the work done by air ...
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2answers
5k views

Relation between work, kinetic energy and potential energy

We derived two equations in class. The work done between two points $A$, $B$ is equal to the difference between the kinetic energy at the last point and the one at the first point. The work done ...
2
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1answer
1k views

Thermodynamic cycles, when is the work negative/positive?

ever since I begun calculating thermodynamical cycles, I've had problems with determining the sign of the work along a particular bit of the cycle. Of course, I guess that an arbitrary cycle is ...
2
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2answers
811 views

Having trouble understanding the work energy principle intuitively

I'm having trouble understanding the work energy principle intuitively. This is what I'm solid on so far: If you have a ball rolling down a hill, it loses potential energy and gains kinetic energy. ...
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8answers
3k views

How can Magnets be used to pick up pieces of metal when the force from a magnetic field does no work?

I learned that the force from magnetic fields does no work. However I was wondering how magnets can be used to pick up pieces of metal like small paperclips and stuff. I also was wondering how magnets ...
4
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2answers
990 views

Is any work done when I walk?

I am trying to figure out the amount of work done when I walk X miles or for X minutes. So I got Work=Force x Distance and Force=Mass x Acceleration and Acceleration=(change in velocity)/time. I am ...
3
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2answers
323 views

How to reconcile the two definitions of work? (mechanical and thermodynamical)

When studying classical mechanics, work is defined as: $W_M=\int F_{tot} \hspace{2 mm} dx$. However, for thermodynamics, work is defined as: $W_T=\int -F_{ext} \hspace{2 mm} dx$. I'm having trouble ...
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1answer
198 views

Adding heat to a system doesn't equal the work done by gas?

So, I answered a physics question for a class that goes as follows: A gas in a cylinder is kept at a constant pressure of $250000\: \mathrm{Pa}$ while $300\: \mathrm{kJ}$ of heat are added to it, ...
7
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2answers
22k views

Conceptually, what is negative work?

I'm having some trouble understanding the concept of negative work. For example, my book says that if I lower a box to the ground, the box does positive work on my hands and my hands do negative work ...
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4answers
196 views

Short-duration forces

In circular motion, it is said that the centripetal force acts only for a very very short period of time, hence is able to only change the direction but not magnitude of the velocity. Similarly in a ...
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2answers
330 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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1answer
2k views

Work done by Static friction

Here $v1$ is relative to the block on which sphere is pure rolling but static friction isn't $0$ as of now . In the following diagram, is work done by static friction $0$ ?, since the point of ...
2
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6answers
613 views

Centripetal Force Acceleration

In uniform circular motion, acceleration is $\frac{v^2}{r}$ and time which it acts $\rightarrow 0$. So $\Delta v = 0$, but then why/how does direction change, when the acceleration should be ...
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1answer
299 views

First law of thermodynamics?

The first law says that the change in internal energy is equal to the work done on the system (W) minus the work done by the system (Q). However, can $Q$ be any kind of work, such as mechanical work? ...
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4answers
773 views

Violation of Newton's Second Law (?) [closed]

Here the big circle denotes the circular path of a stone (small circle on path) tied to a string from the centre of the circular path. This is COMPLETELY HORIZONTAL At an instant the velocity in ...
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6answers
1k views

Electrostatic Potential Energy Derivation

How is the boxed step , physically as well as mathematically justified and correct ? Source:Wiki http://en.wikipedia.org/wiki/Electric_potential_energy As work done = $- \Delta U $. for Conservative ...
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2answers
1k 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 nC(cons. volume)dT = -PdV when deriving the relationship between T and V for an adiabatic process, ...
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5answers
4k views

Workdone in an equipotential surface is zero?

An equipotential surface is one in which all the points are at the same electric potential. If a charge is to be moved between any two points (say from point A to point B) on an equipotential surface, ...
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1answer
267 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 $\mu_k$. ...
2
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1answer
213 views

Work done by gravity on Water

Now according to me we would see change in potential energy of system and equate it to the work done by gravity. But when we see this the first column lowers by $H/2$ and right one rises by $H/2$ ...
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1answer
88 views

Work done by complex field on complex plane

A force field is given by $F = 3z+5$. Find the work done in moving an object in this force field along the parabola $z = t^2 + it$ from $z = 0$ to $z = 4+2i$. I don't understand why conjugate ...
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4answers
635 views

How do you tell what forces do no work?

The total mass of the children and the toboggan is 66 kg. The force the parent exerts is 58 N (18 degrees above the horizontal). What 3 forces/ components do no work on the toboggan? I said the ...
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2answers
776 views

About the work done by gravity to pull the object down to the earth surface

The following question is from an physics exercise and I know the answer and the way to solve the problem but just curious why my own way doesn't work. The question is asking "A 2500kg space vehicle, ...
1
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1answer
2k views

Work done by friction

Suppose we have a block of mass $M$ and we are moving it up a curve, very slowly ($a=0$). The surface is not smooth, and coefficient of friction is $\mu=\mu_s=\mu_k$. To move the block we apply a ...
3
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1answer
231 views

Intuition behind Work

I have a doubt in understanding the intuition behind the concept of work. First of all, I think this isn't duplicate, I've searched on the site, and the closest thing I've found was this post which is ...
3
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1answer
3k views

How to understand the work-energy theorem?

How to understand the work-energy theorem? I took a short lecture on physics for engineering last week. The lecturer emphasized that the work done on an object will cause the kinetic energy change as ...
1
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1answer
198 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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1answer
797 views

Work as an integral of mass over velocity?

As I've understood it, the area under $F$-$s$-graph is the work done, so then :$$W(s)=\int{F(s)ds}$$ I am also given this equation ($W_k$ is kinetic energy, which is equal the work done to set the ...
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3answers
993 views

Integration by parts to derive relativistic kinetic energy

I have come across a weird integration during derivation of relativistic kinetic energy. Our professor states that i can get RHS out of LHS using integration by parts: $$ \int\limits_0^x \! ...
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0answers
110 views

How to solve state parameters using these givens for an ideal gas?

In a thermodynamic turbine using air as an ideal gas, given that you have a known inlet temperature value $T_i$, a known exit pressure value $P_e$, a known inlet and exit velocity $V_i$ and $V_e$, a ...
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2answers
1k views

Finding maximum speed in a work-energy problem

I have the following problem: The Royal Gorge bridge over the Arkansas River is $310\text{ m}$ above the river. A $57\text{ kg}$ bungee jumper has an elastic cord with an unstressed length of ...
7
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3answers
994 views

Energy equation for an open system

I teach undergraduate thermodynamics and I was quite ashamed that I couldn't explain to a student, the following. I thought I'd bring it to physics.SE in hope of providing my student a good ...
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0answers
88 views

Problem in average height

Let, diameter of cylinder hole of height 30m and diameter 2m filled with water. In a book, when author tried to find out the power for lifting all of the water then he used average height. why is ...
3
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2answers
431 views

Find work done by force along a path - is parameterization the only way?

$F = x^3y^4 \hat i + x^4y^3 \hat j$ from $(0,0)$ to $(1,1)$. I am given different paths. For example, "first along x axis and then along the y axis" is one of the paths. Is this problem solvable ...
4
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3answers
210 views

When can one write $a=v \cdot dv/dx$?

Referring to unidimensional motion, it is obvious that it doesn't always make sense to write the speed as a function of position. Seems to me that this is a necessary condition to derive formulas ...
4
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2answers
151 views

Conservative Force and $1/r^2$

Does the inverse square law have anything to do with conservative behavior of the central forces?
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2answers
205 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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2answers
1k 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 ...
3
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4answers
1k views

Paradox- Object thrown parallel to the ground will never fall down

Suppose an object is thrown parallel to the ground. The gravity acts downward (ie. perpendicular to the direction of motion of the object). The work done by gravity on that object will be given by : ...
4
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5answers
4k views

What is $vdp$ work and when do I use it?

I am a little confused, from the first law of thermodynamics (energy conservation) $$\Delta E = \delta Q - \delta W $$ If the amount of work done is a volume expansion of a gas in, say a piston ...
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2answers
354 views

Measuring work done by gravity over non-constant gravitational acceleration

A question from an example from a MIT Classical Mechanics Lecture on Work. Here's the given definition for gravitational potential energy (~32:00): "The ...
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3answers
3k views

Is the normal force a conservative force?

Most of the time the normal force doesn't do any work because it's perpendicular to the direction of motion but if it does do work, would it be conservative or non-conservative? For example, consider ...
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2answers
3k views

Work done by the air resistance [closed]

A ball of mass 0.37 kg is thrown upward along the vertical with a initial speed of 14 m / s, and reaches a maximum height of 8.4 m. a) What is the work done by air resistance on the ball? b) ...
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3answers
320 views

Can endergonic reactions occur outside of living organisms?

If the Gibbs free energy equation is defined as: ∆G = ∆H - T∆S And the amount of energy/work released from a reaction is: ...
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1answer
496 views

Is resistance to motion directly proportional to the speed of a moving object?

Power is known to be equal to the force x velocity (P=FV). Im solving a question that states the following : Car with engine working at 32 kW, mass of 1 tonne, travels at a constant speed of 40m/s ...