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Questions tagged [work]

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

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120 views

Equal forces on masses traveling unequal distances: where is the mistake in this reasoning?

2 identical objects are moving with different constant velocities. Then, in turn same forces act on them for some period. Both times, the same amount of energy is used to produce those forces. As the ...
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6answers
104 views

Why is the total work done on an object its change in kinetic energy, but not change in total energy?

We have just started learning so explain simply. We don't know about conservative or non conservative forces. We are just learning basics.
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2answers
35 views

How can a system of Atwood machine lose gravitational potential energy?

The heavier block in an Atwood machine has a mass twice that of the lighter one. The tension in the string is 16.0 N when the system is set into motion. Find the decrease in the gravitational ...
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0answers
25 views

If a climber was to fall and the load was 50kg, what would be the work done by a 10m rope if it could also stretch an additional 1m? [closed]

Is it essential in finding the work done that the displacement of the force is 11m or is the displacement of the force 1m?
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2answers
28 views

Spring force potential energy and work done

Is the work done by external constant force = to potential energy stored in the spring. i.e. $Fx=\tfrac{1}{2}Kx^2$ But we know $F=kx$ but then $Fx = Kx^2$
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2answers
45 views

Why is the work done by friction zero when body is rolling? [duplicate]

Why is the work done by friction zero when body is rolling? Does it mean no energy is dissipated by friction.
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1answer
69 views

Why use Work-Energy Theorem here?

My confusion is in reference to the solution of this problem, whose problem statement and its solution I restate here: Problem: Two blocks of masses $m_1$ and $m_2$ are placed on a rough ...
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4answers
63 views

Work when there is more than 1 force

I know that for an object with an applied force, the work done is $$W = Fd \cos \theta.$$ I was wondering what would happen when there is another force (e.g. friction)? Is it better to say that the ...
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0answers
52 views

Calculation of the work of liquid thermal expansion. Carnot or fluid dynamics? [closed]

In theory, we have non-flexible tank, and it is filled up with liquid. The tank is connected to the turbine. The turbine has a load: When the pressure rises above 101 bar(abs), it starts to rotate. ...
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2answers
30 views

Thermodynamic costs of implementing real heat engines and how to analyze them [closed]

There are several well-studied cycles, like the Carnot, Otto, etc., among infinitely many. But, what happens when we also consider the costs of driving the system through a particular cycle? How does ...
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5answers
2k views

How can friction do no work in case of pure rolling?

I have read various answers , on PSE and elsewhere , and most of them explain that the point of contact of the rolling object undergoes 0 instantaneous displacement in the direction of friction, I ...
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1answer
48 views

Why isn't electric potential infinite?

In my textbook, I've read that electric potential is the work performed to carry one unit of positive charge to electric field from infinite distance. We know that, W = Fs So here the distance is ...
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2answers
49 views

Direction of work done in gravitational field

For an object that is at a distance $R$ from the earth core, if we want to move it further away to a distance $R+A$, we will do positive work on it since the direction of displacement is in the same ...
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2answers
57 views

What work is done by the wall when a ball hits it?

So, in my physics textbook it's written that the kinetic energy possessed by a body is equal to the amount of work done by an opposing force to stop the body, now that got me thinking that when a ball ...
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2answers
68 views

What is the justification for going from $\frac{d(v^2)}{dt}dt$ to $d(v^2)$ in this derivation regarding work in the presence of kinetic friction?

I do not understand what is being done in the last line of the quote, where we manipulate one integral to get another. Incorporating Newton's second law $\Sigma\mathbf{\vec{F}}=m\mathbf{\vec{a}}$ ...
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5answers
89 views

Work done in the presence of gravity

Consider a system where a block is to be raised from the ground to a height of 1 meter above the ground. It is given that when the force acting on the block and its displacement act in the same sense, ...
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8answers
6k views

Does it take energy to move something in a circle?

Work can be calculated by $W = Fd\cos\theta$ where $\theta$ is the angle between the force $F$ and the displacement $d$ Let's say there's a ball and a (physically ideal - no friction etc.) robotic ...
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4answers
115 views

On Work and Energy [duplicate]

I saw in my class that work done on an object is the energy transferred by a force. Energy is the ability to do work. question 1) Why is this definition so roundabout? question 2) How exactly does a ...
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1answer
29 views

Is there any physically sound argument about why we are allowed to interpret $\dot{\vec p}$ as another force in D'Alembert's principle?

In Analytical Mechanics, when we derive the D'Alembert's principle for dynamical systems, we generally argue as; Since $\vec F^{ext} = \dot{\vec p}$ by Newton's second law, we can interpret it as if ...
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1answer
33 views

Work done by a force in such a situation [closed]

We apply a force on a point on an object such that the point of application moves on the object but the object itself doesn't move. Then is the work done zero or will it have some value?
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1answer
29 views

Heat flow for an ideal gas in Isothermal Expansion

I'm having a bit of difficulty grasping the concept of heat flow in isothermal expansion -- most likely because I don't fully grasp the concepts yet. We were given a problem that the professor ...
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3answers
53 views

Work done on a gas enclosed in a container

According to everywhere work done on system of a gas is equal to $p\,\mathrm dV$ but here $p$ is just the external pressure. Shouldn't internal forces be considered while calculating work done thus ...
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3answers
137 views

Classical Mechanics: work

This a a fragment from my Theoretical Physics (- Classical Mechanics) notes: $$W_{1 \to 2} = \int_{t_1}^{t_2} \boldsymbol{F}\cdot\boldsymbol{v}\,dt = m \int_{t_1}^{t_2} \dot{\bf{v}}\cdot{\bf{v}}\,...
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2answers
93 views

How do voltmeters measure work done over a component?

In my physics class, we were shown the picture below to measure the current and potential difference through a component. We were told that the resistance of the ammeter is as low as possible, and the ...
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3answers
79 views

Why am I getting two answers from the same question? [closed]

In this problem, if I use the formula for power as $\frac{F\cdot s}{t}$, then the answer is 37.5 W. But if I use the formula $F\cdot v$, then the answer is 75 W. How is it possible that the man has ...
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2answers
29 views

$p$-$V$ diagram and internal energy

I recently learned that if the initial state is equal to the final state in the $p$-$V$ diagram then the internal energy is equal to zero so that means $Q=W$. My question is how can you know that only ...
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1answer
22 views

Does the force on magnet depend on coil, when it is being moved relative to the coil?

I am new to electo-magnetism, so i prefer simple language, the problem is: When we move a magnet relative to a coil such that one of its face is towards or at the coil, an EMF is induced in the coil ...
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1answer
17 views

Energy conversions due to movement of car up the slope

We know if a car is travelling at constant speed up the hill then the power output of engine is equal to change in gravitational potential energy per unit time . (Assuming friction negligible). What ...
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2answers
39 views

Confusion on a phrasing of the First Law of Thermodynamics

According to Finn's Thermal Physics Third Edition, the First Law of Thermodynamics is described as: If a thermally isolated system is brought from one equilibrium state to another, the work ...
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4answers
64 views

Friction acting as an internal force

I was solving this problem in my assignment: Assuming a frictional force F acts on the block of mass m, a force -F will act on plank of mass M. Hence, the net work done by frictional force should be ...
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0answers
35 views

Can global unitaries create entanglement?

So I am reading this paper, which states multiple times that: Indeed, global (and thus entangling) unitary operations are capable of extracting more work than local operations from a set of ...
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1answer
55 views

Rotational work done

So the formula for rotation work is $$\mathrm dW=T\cdot\mathrm d\theta$$ where T is torque. While solving a question like in case of a body rolling down an incline (pure rolling), we usully equate ...
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5answers
76 views

Derivation of the work-energy theorem

We state the following version of work-energy theorem : $$ K_2-K_1=Fd=W $$ Where acceleration is assumed to be constant, so is the force $F$. Then the physicists proceed by writing $K_2-K_1=F[x(t_2)...
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0answers
22 views

What exactly are fluctuation theorems used for?

The way I understand is that on the macro scale when talking about quantities such as Heat $Q$ or Work $W$ we can assume that any fluctuations stemming from some particle interaction are negligible. ...
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2answers
44 views

A question on Work and energy in which a body is taken up a hill by a tangential force

The height of the hill is h and length of it's base is l.A force F which is always tangential is pulling the body up the hill. The friction coefficient between hill and body is $\mu$.The body is being ...
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6answers
104 views

If Work=0 for a force along a path, does that mean the force cannot move an object along that path?

Suppose we are given a 2D force vector field $F(x,y)$ (position dependent only, no time dependency) and we're given a path C in the plane, and we compute $\int_C F \cdot ds$ and get zero. I was told (...
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1answer
56 views

Does the First law of thermodynamics hold if the final state is NOT in equilibrium?

So we know the first low of thermodynamics holds for isolated systems $$\Delta E = W+Q\tag{1}$$ Now assuming we are in a thermally isolated system such that $(Q=0)$ we obtain $$\Delta E= W\tag{2}$$...
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0answers
50 views

Is the work function a function? [closed]

The work function is the energy an electron needs to leave the metal. Why is it called a function? Its value is different for different metals, but that doesn't make it a function; density and melting ...
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2answers
54 views

Work done by friction in a plane on a ball

An inclined plane has a rough and smooth surface which are of equal length. A ball is kept at rest at a height $h$ and is then rolled on the surface of the inclined plane. My question is that ...
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3answers
106 views

Possible paradox relating to acceleration, velocity, and work

I recently encountered a question that made me think of this "paradox": Imagine the following situation: There are two forces: Force 1 and Force 2. They accelerate a mass $m$ from the same initial ...
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4answers
91 views

How did we come up with the formula of the work done by a force? [duplicate]

I don't understand why the work represent the change in energy of a system. I understand the work energy theorem but where did we get the formula of the work from in the first place. Also when I ...
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1answer
44 views

Doubt in thermodynamics pressure volume work done

Why work done in irreversible process is not calculated as -$\int p_{internal} dV$ ?
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2answers
67 views

Work done by friction when object is rolling WITH slipping [closed]

So if I have an object that is rolling with slipping like a bowling ball, if I use W=F•dr definition, then work done by friction has to be negative. But if I use the W=τ•dθ definition, then work is ...
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0answers
32 views

Relationship between work and kinetic energy?

Lab Question: What is the relationship between the work done on a car as it rolls down a ramp and its kinetic energy at the bottom of the ramp? We have a 30 gram car that starts above a table and ...
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2answers
53 views

how can internal energy do work?

how can internal energy do work? As far as i know, internal energy is the sum of KE and PE. But how can this, in turn, do work? It would be great if you can give me some scenarios. Thank you.
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1answer
38 views

How does thermal energy in a system do mechanical work? [closed]

Explain that a system with thermal energy has the capacity to do mechanical work. Also, in addition to this what are the differences between work and mechanical work?
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4answers
48 views

Why does the GPE of an object always equal the work done?

I had a question that said, "If you do 100 J of work to lift an object over your head, what is the gravitational potential energy relative to its starting position? What would be its gravitational ...
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5answers
53 views

Work done in lifting a mass vs work done by mass as it falls to starting position

There are variations of this question on here but I was unable to find exactly what I was looking for so please bear with me if this is old hat. If I start with a mass m at rest at height H1 and ...
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0answers
44 views

Maximum achievable mechanical work when heating water

I am doing a question about finding maximum achievable mechanical work when 1L of liquid water is heated from T₁ to T₂ at atmospheric pressure. The solution is $$W = \int_{T_1}^{T_2} \frac{T - T_1}{T} ...
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0answers
21 views

If is work done by magnetic field is 0 then why does 2 magnets attract when kept together? [duplicate]

If 2 magnets are kept close to each other they attract then shouldn't it be considered as work done by magnetic field?