# Tagged Questions

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

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### What is difference between variations of the work and virtual work?

I really want to know whether or not both equations are the same mathematically. I think that they are the same, I just want to be sure. (Reference: this website.)
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### basic question about work exercise [on hold]

I am learning independently from Tobochnik's statistical physics text. He asks a warm up question about work: A person pushes a block up a frictionless ramp. Is the work positive, negative, ...
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### PVC Pipe ideal force [on hold]

A longbow is made with a string which is not stretchable and is made with a PVC pipe of radius of around 1 centimeter on the outer and 0.8cm on the inner radius. The pipe is 120 centimeters and the ...
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### Does displacement affect force? [on hold]

I am sorry for being unclear with my previous question. The main topic of the experiment we conducted was about work. As we learned: $W = Fd$ Work, from my understanding, is the product of work and ...
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### Simple Disk rolling with slipping on a horizontal plane

This is the first time I've encountered this scenario. I want to understand how to handle it. Since the disk is slipping, what would be the work done by the frictional force? What is the ...
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### Work done by internal forces of a rigid body

I am reading Goldstein's Classical Mechanics book, and I came across that: In a rigid body the internal forces do no work Is this statement based on the assumption that the internal forces are ...
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### Conservation of Energy with Rotation Caused by Friction

A book that I am using to study poses the following problem: Suppose you wish to use a spring with a force constant $k$ to launch a spherical ball or radius $r$ and mass $m$ up a ramp of inclination ...
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### Is energy only transmitted through electromagnetic and particle radiations? [closed]

Which are the other ways of transmission if any? If energy does not require any medium for transmission(as for sunlight reaching earth, the heat too), is it transmitted in quanta in particle radiation ...
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### Isobaric process with non-boundary work?

I came up with a doubt on isobaric processes. Firstly, in any isobaric process, (irreversible or not) the following hold $$Q=n c_p (T_B-T_A)\tag{1}$$ $$W=p (V_B-V_A)=n R(T_B-T_A)\tag{2}$$ Is that ...
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### Principle of Maximum Work for Different Paths

The principle of maximum work states that for any process between two states, the work done by the system is maximised for a reversible process (and heat transfer is minimised), and that the work done ...
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### Is the work done by gas necessarily positive if the cycle is travelled clockwise in the $P-V$ plane (and viceversa)?

Is it always true, for any cycle followed by a gas, that, if the cycle is "travelled" clockwise in the $P-V$ plane then the work exchanged by the gas is positive, and viceversa for the clockwise ...
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### Does the thermal efficiency depend on the reversibility of the engine when isochoric or isobaric processes are involved?

I'm confused on the efficiency of a thermal engine (with an ideal gas) in the case in which it is reversible or not reversible, in particular where the ideal gas follows isochoric or isobaric ...
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### Is it equally difficult to lift something as it is to lower it?

This just seems a bit counterintuitive cause lifting stuff seems harder, but if I do them at the same, constant speed, I will apply the same force opposing gravity, just over opposite displacements, ...
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### Gravitational potential energy defined in terms of work

An outcome of my high school syllabus is to "define gravitational potential energy as the work done to move an object from a very large distance away to a point in a gravitational field: $-GMm/r$". ...
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### Mistake calculating electrostatic potential energy formula!

I have a problem calculating the electrostatic potential energy. I rely on these equations coming from mechanics: U_{B}-U_{A} = -W_{A \ \rightarrow \ B} (done\ by \ the \ field \ ...
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### Resources on how to estimate the power density of gravity?

If a drop a ball from a height $h$, the work done by gravity (in this particular situation $i$) is $w_i=\int_0^h F_G \cdot dl \approx mgh$. What I would like, is to estimate the work done by gravity ...
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### How to compute work needed to build a configuration of charges

Suppose an alignment of four charges in the vertices of a square. The first pair on one diagonal has positive charge and the other negative charge, all charges are of the same absolute value. length ...
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### Conventions for work and energy are not going correct in this situation [closed]

Let us consider 2 objects A and B. The initial PE of the objects be U(A)=10J and U(B)=0J. Let F be the force exerted by A on B. Suppose W be the work done by force F. Due to this the PE of both the ...
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### Work done in thermodynamics [duplicate]

The work done in thermodynamic process is given by the integral of Pdv and also we can write so assuming a quasi static process between two points. But this work is then non dissipative work or work ...
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### Electric Potential produced by Hollow Sphere

Let there be a hollow sphere (Throughout the question we will ignore the thickness of the sphere) which is positively uniformly charged,q of radius, R. Suppose there to be a test positive charge, q' ...
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### Efficiency of engine in the case non-boundary work done on the system

The engine efficiency is defined as $$\eta = \frac{W_{\mathrm{produced}}}{Q_{\mathrm{absorbed}}}\tag{1}$$ But suppose that, in one of the processes that takes place in the cycle of an engine that ...
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### Can the work in a isochoric process be non-zero?

I came up with a doubt regarding isochoric irreversible processes. Question: Is it always true that, for any isochoric process, reversible or not, the work exchanged by the system is zero and the ...
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### Potential Energy = mgh. What is the name of this principle and did Newton discover it?

Somebody I know keeps trying to convince me that Potential Energy $PE=mgh$ is one of Newton's Laws (as well as the closely related idea, Work Done = force x distance moved). I am fairly certain that ...
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### Frictional torque=? [closed]

A uniform, hollow, cylindrical spool has inside radius $R/2$, outside radius $R$, and mass $M$ (see figure below). It is mounted so that it rotates on a mass less horizontal axle. A mass m is ...
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### Is reversible work a point function?

The potential of a conservative force is equal to the reversible work done on or by a system. But since the potential of a conservative force is represented by a point function, this would seem to ...
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### Work done by an ideal gas expressed as change in potential energy of fluid

I get confused in problems where it is necessary to evaluate the work done by a gas that someway moves a mass. I'll make an example. Consider the tube containing mercury and an ideal gas in A (...
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### Work done on gas problem with movable set

I found two different version of an exercise where the work is considered in a different way. Consider a gas in a tank divided in two parts by a movable set. The set in $B$ is also movable. If a ...
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To calculate work done by general force, apparently we have integral like the following: $W=\int_{s_1}^{s_2} F(s)\,ds$ But why when it comes to the spring, it is not $W_{s}=\int_{0}^{s} Fs\,ds=\int_{... 2answers 35 views ### Work and energy example [duplicate] The normal definition of Work, as far as I have read, is: Energy is transferred through work. But I just heard an educationist state this example, where there is a weightlifter who keeps up a huge ... 0answers 34 views ### Joule's “Work-Heat Equivalent” Experiment I have been reading about the Joule's experiment that is supposed to have shown that work is the equivalent of heat. I can't really find the original paper and I am finding trouble understanding how ... 0answers 15 views ### Calculating the amount of work done for a bench press movement? Is this a reasonable conclusion? Me and a friend have been working out for some time and have been bench pressing each weak, increasing our weight. Once we started getting to heavier weight we noticed that he was able to get more ... 2answers 44 views ### Relation between field and Potential energy of a body I have read that if a body is in a field and is 1. moved in a direction opposite to the direction of a field, its potential energy increases.But why does it increase? 2.Also, if we move the body in a ... 1answer 46 views ### Work done relation to potential energy I know work done is negative of change in potential energy, I.e.,$W=-(∆U)$. It means that Work done against a force (or work done on a system) increases its potential energy. And Work done by a ... 2answers 48 views ### Negative work leading us to negative energy [closed] We know that energy is the ability to do work and we know that the work can be negative as cos theta of the angle in which force is applied can be negative. Moreover we take the units of work and ... 2answers 55 views ### Virtual Work- Is the presentation in Cornelius Lanczos wrong? Book: The Variational Principles of Mechanics by Cornelius Lanczos Edition: 4th Chapter: 3, The Principle of Virtual Work I am on the second page of the 3rd chapter (pg 75; it has the Eqn. 31.1). ... 3answers 42 views ### Need help with signs (+ -) in electric potential work and potential energy problem The problem is from Sears and Zemansky's University Physics, 12th edition in Spanish. The problem says: How much work is needed to assemble an atomic nucleus that contains three protons if it is ... 1answer 34 views ### Conservation of mechanical energy when object strikes the ground When I raise a pen, the external work I do gets stored in the form of potential energy hence the mechanical energy is increased. When I leave the pen the pen starts falling and as the potential energy ... 2answers 69 views ### Work done according to Newton's Principia Actually I was going through the principia, reading Newton's derivations of the properties of ellipses. Suddenly I had this question which got stuck in my mind - Throughout Principia Newton uses the ... 3answers 85 views ### Is this definition of work right? My thermodynamics textbook defines work as follows. Work is motion against an opposing force. But this definition of work doesn't imply that work is done in accelerating a body does it? So is ... 4answers 65 views ### Is the concept of work only defined in mechanics? I'm studying energy and work, so far it looks like work only makes sense in kinematics (objects that move), but energy makes sense in many other ways (electric, thermodynamic, mechanic). Is work a ... 3answers 69 views ### What is the relation between Force, Physical Strength,Enery and Work? I am sorry ,but, I am not much of science or a physics guy, if this question sounds stupid. Anyways, what is the relation between all of them. Like for example, does applying more force means more ... 2answers 70 views ### Why does the sign of Delta H indicate whether the reaction is exothermic or endothermic? If$\Delta H = Q + W$(assuming constant conditions), then there are two terms involved in calculating$\Delta H$, only one of which measures heat gained/released. It is possible then for$\Delta H$... 4answers 51 views ### How can removing energy from a system do work? (ice) Water freezing into ice expands, damaging roads, breaking rocks, etc. To my understanding, this is doing work (in a physics sense) by removing energy from the system. How is this possible? 1answer 39 views ### Thermodynamics: efficiency of a heat engine [closed] How can we calculate efficiency of a real heat engine? Do we have to consider volume of an object while calculating efficiency? Like in this question If so, how we have to proceed? Thanks in ... 0answers 39 views ### Why we can use partial derivatives to tell if a force is conservative? [duplicate] Let us, initially, analysis only a two dimension situation. Assume that$F(x,y)$is a force dependent on the particle position (give by$x,y$) is proposed that if \frac{\partial \... 1answer 31 views ### Why is force negative if PE increases? I'm looking at the PE vs force graphs for gravity, and it doesn't make sense to me. As potential energy increases (and the object goes higher above the ground), F=-mg. But if I'm raising an object up, ... 1answer 61 views ### Work done in bringing down a body [closed] A block of mass$30$kg is being brought down by a chain. If the block acquires a speed of 40.0 cm/s in dropping down$2.00$m, find the work done by the chain during the process. I have calculated ... 1answer 78 views ### What does$P = Fv\$ mean? [closed]

The engine of a car is developing a power of 90kW when it is moving on a horizontal road at a constant speed of 100 km h−1. Estimate the total horizontal force opposing the motion of the car. I ...