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

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-2
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1answer
76 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
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1answer
57 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
63 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
106 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
33 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
38 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
161 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
28 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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2answers
56 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
28 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 test ...
0
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0answers
27 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
68 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
votes
1answer
55 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 ...
5
votes
2answers
107 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
votes
2answers
61 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
30 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
155 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
vote
2answers
53 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 ...
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
votes
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
80 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
69 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
41 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 force ...
0
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0answers
30 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 F\...
1
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2answers
59 views

How does conservation of energy work?

I understand that the law of conservation of energy states that energy cannot be created or destroyed, it can only change from one form to another. This means that the total energy before a certain ...
3
votes
2answers
204 views

Climbing Stairs and Calories Burnt

I climb stairs to work (20 floors) every day . The least amount of work my body is doing by gaining potential energy (P.E) = mgh where m is mass , g is acc. due to gravity and h is height . Assuming ...
0
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2answers
43 views

Relationship between work and energy in an electrostatic system

I am having problems understanding the relationship between the concepts of Work and Energy in a electrostatic system. As I know, the definition of Potential Energy is the ability to do work. In a ...
-1
votes
2answers
86 views

How can work be done during collisions? [closed]

Consider a collision between two material points, with no external forces acting on the system. Linear and angular momentum of the system are always conserved, while the kinetic energy of the system ...
1
vote
3answers
61 views

Work energy theorem: variation of kinetic energy as sum of terms given by the work of single forces

Work-energy theorem states that $$W_{\sum F_i}=\Delta K,$$ where I expressed with $W_{\sum F_i}$ the work done by the resultant of forces ${\sum F_i}$ and with $K$ the kinetic energy. In general it ...
0
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3answers
93 views

Lifting and putting down a weight

A man in a gym lifts a weight and then puts it down where it was before. 1) What can be say about the work done by the man to the weight? 2) Can it be equal in absolute value to the work made by ...
0
votes
2answers
17 views

Electric potential energy of a charge

Potential energy is the work done by the particle against a conservative force. Isn't it? when a charge is fixed on a free space and then when we bring another charge from infinity to a distance r ...
2
votes
2answers
6k views

Does a force do work on an object with constant velocity?

I know that a force does no work on an object if the object's displacement is zero, but if an object is moving at a constant velocity $\bar{v}$, and a force $\bar f$ (let's say that $\bar f$ and $\bar ...
2
votes
2answers
885 views

Work done by a non-conservative force and change in potential energy

I know that the work done by a non-conservative force is equal to the change in total mechanical energy (from Work-Energy Theorem). But I read in a place that "Non-conservative forces don't affect PE"....
1
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2answers
91 views

Physical meanings of kinetic energy

While studying energy on Sears & Zemansky's University Physics, I came up with a doubt on the meaning of kinetic energy. The book gives two possible physical interpretations of this quantity. ...
1
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1answer
64 views

Work-energy theorem for a system

While studying energy conservation on Morin I found this explanation about the work-energy theorem for a system. The work–energy theorem stated before is relevant to one particle. What if we are ...
0
votes
1answer
35 views

Directional derivative of the potential energy in the direction of the displacement in three dimensions

For a conservative force $\vec{F}=-\vec{\nabla } U \implies \mathrm dW= -\vec{\nabla} U \cdot \mathrm d\vec{s} $ Where $\mathrm d\vec{s}$ is the infinitesimal displacement. For a differentiable ...
0
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1answer
43 views

Work done by a force

What is the difference between work done by a force and work done against that force? Is it true that work by a force = -(work against that force)?
0
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1answer
36 views

How would you get the velocity in this problem? (and what did I do wrong) [closed]

This problem is supposed to be solved by using the conservation of energy but I do not really know how to solve it that way.
5
votes
2answers
7k views

Work done by isothermal expansion from two different viewpoints

Consider an adiabatic system as follows. It consists of a gas in a container and a piston. Initially, the system is at equilibrium and the gas inside it occupies a volume $V_i$ at a pressure $p_i$ ...
1
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0answers
21 views

Kinetic energy vs Kinetic Energy scenario in a collision, mechanical energy used for work?

Most collisions have Kinetic energy conserved or in the case of inelastic collisions energy is lost into other forms. Though the equation of "TMEi + Wnc =TMEf" is true however, what if two unequal ...
0
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0answers
26 views

Microscopic Definition of Heat and Work

If I am given a statistical System, then I can define state-variables like Energy, Entropy or other Observables, and then I can (at least for equilibrium states) give the Change of Energy as: \begin{...
0
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1answer
19 views

About Electric potential

when we bring a unit positive charge from infinity to a point in the electric field EF does work on the charge and external work is also done on the charge in same amount but in opposite sign. then ...
1
vote
3answers
184 views

Is work-kinetic energy theorem useless?

This is how my book explains it: $W_{net} = \delta K$ Since the net work is tied to changes in kinetic energy and changes in speed, a mass must accelerate in order for net work to be nonzero. ...
1
vote
2answers
11k 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 ...
1
vote
1answer
44 views

Work done by friction on a conveyor belt [closed]

At a factory, a 300-kg crate is dropped vertically from a packing machine onto a conveyor belt (I apologize for not having a picture) moving at a speed of 1.2 m/s. The coefficient of kinetic friction ...
8
votes
4answers
431 views

Is work done by a pseudo force?

If a body is viewed from the frame of another body which is itself accelerating, will work be done by the pseudo force acting on the first body in the frame of second body ( provided the first body is ...
2
votes
3answers
60 views

Using thermal expansion for mechanical work

Assume I could heat up a bar with zero heat loss to the environment. I could then use the thermal expansion to do some work, for example compress a gas. Where does the energy needed for the ...
1
vote
2answers
52 views

Condition for a force to be conservative

I get that a force dependent on path is non-conservative or a force which does non-zero work in completing a cycle. But how do you prove that mathematically. Let's assume I have a force F= 2yi + ...