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

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-3
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0answers
36 views

Conservation of mechanical energy [on hold]

Think of a case where non-conservative force does positive work. In this case, my teacher said that mechanical energy will not change. But work done by non-conservative force = total final ...
2
votes
2answers
52 views

Dissipation and first law of thermodynamics

Consider the following situation: a certain gas is contained in a well-insulated cylinder with a well-insulated piston head. Now, in this case the piston is not frictionless. In order for the piston ...
1
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4answers
60 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 ...
0
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3answers
77 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 ...
1
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3answers
64 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 ...
1
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1answer
137 views

Work done by friction on a body?

I know that when a body slides over a surface, the work done by friction is not stored as potential energy in the body. It is dissipated in the form of heat. But why is it not stored as potential ...
0
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0answers
14 views

Wind turbine impact on cars fuel consumption [closed]

I'm struggling with one physics question. I would like to know approximately how much cars fuel consumption rises(liters per 100km) besides normal driving if I attach wind turbine to cars body. I ...
8
votes
5answers
16k views

Why does work equal force times distance?

My 'government-issued' book literally says: Energy is the capacity to do work and work is the product of net force and the 1-dimensional distance it made a body travel while constantly affecting ...
0
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2answers
61 views

Problems with work on an inclined plane

A constant force $F_a$ of magnitude $82.0N$ is applied to a $3.00 kg$ shoe box at angle $53.0^{\circ}$, causing the box to move up a frictionless ramp at constant speed. How much work is done on ...
0
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3answers
282 views

Work and free body diagrams

I am a bit confused with how to find work when there is a free body diagram. I am trying to work out this problem, and in it a box is being pulled at a constant speed by a rope at a constant angle ...
1
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2answers
53 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 $\Delta H$ ...
1
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1answer
19k views

How much work is needed to compress a certain volume of gas?

I want to know the formula (and what does the symbols stand for) for how much work is needed to compress a certain volume of gas?
1
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4answers
45 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?
-1
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1answer
32 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 ...
3
votes
4answers
233 views

How to calculate the work of the electrostatic forces in a parallel-plate capacitor?

The expression of the energy stored in a parallel-plate capacitor is: $$U = \frac{e_0\cdot A \cdot V^2}{2d}$$ with $e_0$ the vacuum permittivity, $A$ the surface of the capacitor, $V$ the applied ...
1
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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 \begin{equation} \frac{\partial ...
0
votes
1answer
24 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, ...
2
votes
1answer
60 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 ...
-2
votes
1answer
68 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 ...
0
votes
1answer
52 views

Why is standing still easier than walking? [closed]

Both the works basically push force into the ground.So why does walking require more work?
0
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1answer
62 views

Understanding work with rotational momentum/moment of inertia

Apologies for the basic question but between the vectors and the spinning, I'm getting confused. If I have a wheel with moment of inertia $I$ spinning at some rate $\vec\omega$ around an axis, what ...
0
votes
1answer
98 views

Why does holding an object cost energy while no work is being done? [duplicate]

I was reading the discussion here: Why does holding something up cost energy while no work is being done? I feel as though the question is being avoided. Suppose instead of holding an object by hand ...
0
votes
1answer
30 views

How to calculate impulse required to move an object vertically upward by given distance [closed]

Suppose I have a stationary object of mass $m$ and I want to apply a momentary force in the vertical direction so that it just reaches the height $h$. So how do I calculate the impulse required in ...
0
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1answer
29 views

What is the work done by battery and what does work done on battery mean?

Suppose we have a charged capacitor connected to a battery. Now we push the plates of the capacitor away from each other decreasing capacitance and hence energy stored in the capacitor decreases. Now ...
0
votes
2answers
157 views

I dropped my tissue box on a glass table, the box didn't bounce back, table didn't move nor break, what happened?

I have a box, it drops and thus by moving has Kinetic energy, It doesn't penetrate and impacts however the box doesn't rebound nor breaks the table. Its like when I slam my fist on a table but the ...
0
votes
1answer
27 views

How does an object with gravitational energy exhaust that energy as work?

To my understanding (which is pretty basic) energy is the ability to do work. The higher objects are above a point - more gravitational energy they have relatively to that point, which means that they ...
2
votes
0answers
23 views

What is happening to energy that is not used as work? [duplicate]

To my understanding (which is pretty basic), energy is the ability to do work. But if for example, I push a wall, I do exhaust my energy, but no work is done since the wall is not moving. So what is ...
0
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3answers
142 views

Does the work done by a person equal the work done on the object in this situation?

If you applied a constant force over a floor that has friction on an object, would the work done by the person equal to the work done on the object? Assume that the floor is flat and that the object ...
0
votes
2answers
52 views

How does kinetic energy do work? [closed]

To my understanding, work is done on object A when object B is applying a force on object A, causing object A to displace. Since energy is the ability to do work, what work does a moving object do, ...
0
votes
1answer
26 views

Electric potential and work

A unit positive charge $q$ is placed in an electric field caused due to a positive charge $Q$. $q$ experiences force of repulsion $F_R$. We apply an external force (FEXT) opposite to $F_R$. The ...
1
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1answer
238 views

Potential energy of springs and gravity, and work of a force

I am currently really stuck on this problem and I am not sure how to actually solve it, I think I can reason it out logically but I do not know how to show it. Here it is and under I will show what I ...
0
votes
0answers
19 views

Magnetic force on an iron nail

Work done by a magnetic force is zero but the why iron nails are attracted towards a magnet. The fly towards a magnet so the gain K>E i.e work has been done on them. I know its not actually the ...
0
votes
1answer
67 views

Is $\mathrm d(PV)$ the same with work received OR produced?

When I write energy conservation in thermodynamics problems, I write the internal energy before, the pressure energy before (so these two are the enthalpy) and then I add/substract the work and heat ...
0
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1answer
53 views

Solenoidal forces

As far as I know a solenoidal vector field is such one that $$\vec\nabla\cdot \vec F=0.$$ However I saw a book on mechanics defining a solenoidal force as one for which the infinitesimal work ...
1
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3answers
617 views

Is net work and total work same?

According to my text book Total Work = Delta Kinetic Energy = KEf - KEi But then work is defined to be dot product of Force (vector) and Displacement (vector). Also to my knowledge work is ...
5
votes
2answers
100 views

How is the dot product a generalization of multiplication?

I've seen an interesting explanation for lots of what I previously thought were unmotivated definitions in Newtonian mechanics, namely that power is always defined as effort times flow. But when ...
0
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2answers
59 views

Free Expansion Of and Ideal Gas

We know that in free expansion of an ideal gas, no heat enters or leaves the system. We also know that $P_\text{initial}V_\text{initial}=P_\text{final}V_\text{final}$ is valid. If heat exchange ...
0
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2answers
28 views

Trouble understanding non-conservative force and work

I am having some trouble defining whether a force is conservative or not. In the example that we are working on a mass on a pulley system is used to cause a slender bar to rotate from rest to a ...
3
votes
6answers
151 views

When we write that $F = -\nabla V$ , what would happen if we ommit the (-) minus sign

I have had this question for a long time. In classical mechanics, if we choose $\mathbf F = -\mathbf \nabla \, V,$ with the minus sign, we can proof the work - kinetic energy theorem. What are the ...
1
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2answers
40 views

How can you tell if the work done by a force is negative?

This is kind of confusing to me. I'm guessing that it's specific to the problem. Is the work done by friction always negative? Is the work done by gravity always negative? Spring as well? It seems ...
1
vote
6answers
91 views

Why does positive work done by internal conservative forces $\implies$ decrease of potential energy?

Potential energy can be thought as the amount of work that the force can potentially do on the point because of its position. $$W=-\Delta U=U_{initial}-U_{final}$$ A positive work done by a force ...
1
vote
1answer
59 views

Rotational work and forces such as static friction or ropes tension

I'm confused about the rotational work, defined as $W=\int_{\theta_1}^{\theta_2} \tau_z d \theta $ Where $\tau_z$ is the component of the torque parallel to the axis of rotation $z$. Consider a ...
0
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2answers
475 views

Work done by battery and potential energy of a capacitor

I have a doubt about the work done by a battery and the potential energy of a capacitor? 1- Consider a circuit where the capacitors are connected to the terminals of a battery. Through calculations ...
12
votes
4answers
2k views

Why should Conservative forces have their curl equal to zero?(intuition)

There are several conditions that must be met in order for a force to be conservative. One of them is that the curl of that force must be equal to zero? What is the physical intuition behind this? If ...
0
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3answers
7k views

Work, Energy & Power - Body slides down a hemisphere

A small body of mass $m$ slides down from the top of a hemisphere of radius $r$. There is no friction between the surface of the block and the hemisphere. The height at which the body loses contact ...
0
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3answers
79 views

Zero Potential Energy Change in Raising a Mass

Suppose I am able to lift a body of mass $m$ up using a constant force $F=mg$ so that net acceleration is zero on it. I want to find the potential energy and the total energy of the body when I have ...
-2
votes
3answers
63 views

According to Newton's third law the force between two object is balanced when they force exert to each other

According to Newton's third law, the javelin exerts as much force on the athlete as the athlete exerts on the javelin. Would it be correct to say that the javelin does work on the athlete?
0
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1answer
40 views

A conceptual question about work

Consider an object of mass $5kg$ on a plane. If a horizontal force of $10N$ acts on the object for a time interval of a second. Calculate the work done on the object by the force given that the ...
0
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0answers
29 views

Efficiency of a Carnot refrigerator without knowledge of the temperatures

We know that in a Carnot refrigerator we can express the efficiency as $$\eta = \dfrac{Q_1}{Q_2-Q_1}=\dfrac{T_1}{T_2-T_1},$$ where $T_1$ and $T_2$ are temperatures of the reservoirs between which ...
0
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3answers
3k views

Proof that the electric field is conservative

I was told a proof that the electric field was conservative (without using $\nabla$) which used a point charge and showed the following: $$w.d.=\int_c{\vec F \cdot \mathrm{d} \vec l}=\int_c{\vec ...