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

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Work-Energy conservation with friction

I didn't go to the lesson of work-energy theorem, so I miss something about this subject. I know the formulas, but I can't figure it out. This question has many quantities. Here is the problem, ...
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1answer
21 views

Deriving the equation for the speed of a block down an incline using work - keep getting the wrong constant

So the question is: There is a block of mass $m$ travelling along an incline that makes an angle $\theta$ with the horizontal. If the block is pushed up the incline with an initial velocity $v_o$, ...
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36 views

When moving from one position to another at a constant velocity, how does the conservation of energy hold?

I know that this might be a duplicate question, but I have not found any satisfactory answers that clear up my lack of understanding. Here is my question. Say a sloth hangs on a tree in the middle of ...
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2answers
64 views

Lack of rigour in usual derivation of Work-Energy Theorem

The derivation of the Work-Energy theorem usually goes as follows: You define the work done on a particle under net force $\vec{F}$ as $$W=\int\limits_C \vec{F}\cdot\mathrm{d}\vec{r}$$ And then you ...
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49 views

How much work do I need to convert 300ml of water from 25°C to 3°C? [closed]

A question on how to apply thermodynamics principles to figure out how much work is needed to hold 300ml water in room temperature at 3°C. So far I have: 1Cal for each degree per g of water. We have ...
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36 views

Work and energy

when a ball of mass m is brought with uniform velocity from infinity into the g field of the earth at a distance r from it, the potential energy of the ball earth system decreases from 0 to -GMm/r. ...
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1answer
143 views

How did Feynman prove that energy cannot be extracted from electric field?

In the Feynman Lectures, vol. II, chapter 4, Feynman discusses electric potential and says: If we carry a charge from point $a \to b$, $$W = -\int_{a}^{b} \mathbf{F} \cdot ds.$$ Now, in general, ...
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1answer
40 views

Help calculating work done by stretching a wire [closed]

A wire of length 0.89 m and cross-sectional area 1.7 cm2 is stretched elastically by an amount 1.2 cm. By Hooke’s law, the restoring force is $−k\Delta L$. Calculate the work done in ...
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5answers
193 views

How can static friction do work?

By definition, the work done by a force is $W = F\cdot d$, so how can static friction do work? Can this force move the body a distance of $75~\text{m}$?
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21 views

Constant 2 in kinetic energy equation [duplicate]

Trying to understand where the constant 2 comes from in the kinetic energy equation, $mv^2/2$. Why 2 and not another number?
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1answer
54 views

Work done by friction on car

David Morin, in "Introduction to Classical Mechanics" says that friction does not exert a force on a car because the ground is fixed but that KE of the car is changing to internal kinetic energy in ...
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5answers
256 views

when an object is lifted (at a constant velocity) shouldn't the work done on the object be zero? [duplicate]

When I lift an object from the ground (at a constant velocity) I'm applying force on the object equal to its weight and the earth is also pulling it downwards with equal amounts of force. So if the ...
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4answers
113 views

If velocity is constant, how can $p = F\cdot v$ be non zero?

If an airplane of mass $m$ is flying at a constant speed $v$, the power of the airplane is $$P = m\cdot v\cdot g $$ where $g$ is the acceleration of gravity and therefore: $$ F = m\cdot g, $$ but, ...
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2answers
46 views

Why am I getting that work it's always the same in both directions?

I'm studying electrostatic and I'm getting pretty frustrated because with the definition of work I'm getting that it's always positive and it doesn't make any sense. So here I have 2 positive ...
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1answer
46 views

Relativity of Work

Let's say there is a man pushing a wall with a force of $-1 \text N$, and moving it $0 \text m$. Since $W = F \cdot d$, he has done $0\text J$ of work on the wall. Another man is pushing a duck with ...
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624 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 ...
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1answer
64 views

Normal force, work and conservativity

I have searched very much on line, both in this site and elsewhere, but found no proof of whether the normal force is conservative or is not, in general. Clearly, if the force is orthogonal to the ...
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1answer
34 views

The concept of displacement in definition of work

Suppose an ideal spring is attached to a wall at one of its end. Let an external force act on the spring at another end to stretch the spring to distance $x$. If spring constant is $k$ then work done ...
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1answer
57 views

When to use h = Cp∆T or u = Cv∆T

I'm getting myself confused on when to use h = cp∆T or u = cv∆T where cp is the specific ...
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1answer
25 views

How much power does it take to keep a massive particle suspended in a gravitational field?

For instance if I have a rocket of mass $m$ in a uniform gravitational field $g$, and I want to keep it floating in the air via thrust alone, then how much power in the form of (say) chemical energy ...
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2answers
38 views

Use Work-KE Theorem? [closed]

I've been trying so long at this problem to no avail. I drew my free body diagram, but I'm unsure which formula to use. Could someone help me out?
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0answers
22 views

How is the Joule normalised?

Apologies if this question is a duplicate, I tried searching for this question both on Google and here, but was unable to find an answer. A Joule is defined in various ways, some of them being: ...
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1answer
39 views

Work needed to pump the balloons

Let's suppose that we want to pump the balloons underwater from the initial volume $V_0$ to the volume $V_1$. The pressure there equals $p_1$ and the atmospheric pressure is $p_0$. It is claimed ...
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2answers
55 views

How this formula for work follows from the definition?

If a particle moves along a path $\gamma : I\subset \mathbb{R}\to \mathbb{R}^3$ then the work done by a force $\mathbf{F}$ is defined by $$W = \int_{\gamma} \mathbf{F} = ...
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1answer
34 views

Does the line integral definition of Work involve distance or displacement?

My textbook reports the following definition of Work: where ds is the infinitesimal displacement. I know that an infinitesimal displacement is usually denoted by dr and I also know that the ...
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72 views

If an object rests on a table, not accelerating, how much work do both the object and the table do?

Obviously, the net work done is zero, because there's no motion, but is the proper way to look at it that both the object's gravity and the table's normal force do zero work, or that one does positive ...
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1answer
35 views

Integral limits when calculating the work

If I integrate $$dW= \vec{ F} \cdot d\vec{\ell}$$ which are the limits? In $$\int\limits_{W_{inf}}^{W_{sup}}dW= \int\limits_{\vec{\ell}_{1}}^{\vec{\ell}_{2}} \vec{ F} \cdot d\vec{\ell}$$ it is ...
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1answer
39 views

Which is the right sign convention for the potential difference?

The circulation of the electric field gives the potential difference, but is it : $$V_B-V_A = \int_A^B\vec{E}.\vec{dOM} \hspace{1.5cm} (1)$$ or $$V_B-V_A = - \int_A^B\vec{E}.\vec{dOM} \hspace{1cm} ...
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2answers
65 views

Where does this formula for sagging of a beam come from?

In one of my physics textbooks there is a chapter on the elasticity of materials which contains pretty basic outline about Young's modulus, stress-strain, elastic potential energy and related stuff. ...
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3answers
49 views

How work theoretically is zero, when person did do work while covering a distance then returning it?

$W = Fd$, meaning if a body moved a distance, say $3 m$, and returns, its distance will be zero and work will be zero. I do understand it mathematically and graphically but can someone explain it to ...
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53 views

Given Force in vector form, how do I find work done? [closed]

A force of $F=\hat i+2\hat j-3\hat k$ is applied to a particle that moves 10 meters in the direction of $\hat i+\hat j$. How much work is done?
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1answer
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Meaning the symbol, $W$ and $dW$

What's the difference between $W$ and $dW$? They are both work done and have similar formulae (same dimension). But I don't know the difference between them. $dW$ here ISN'T power.
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43 views

Given an initial push, is work done on an object infinite in a hypothetical empty universe?

Consider a hypothetical empty universe containing a single object. Given an initial push, will the work done by the forever moving object be infinite?
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0answers
49 views

How much work can a single grain of rice do? [closed]

I found a website saying a grain of rice contains 1/10 kcal. I'm not a physicist and haven't done maths for a long time. But here's what I came up with: E = m * g * h One small calorie equals ...
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1answer
37 views

Why the gravitation potential in a uniform field has negative values?

As we know the gravitational potential is the work done per unit mass in taking a point mass from zero potential (at infinity distance) to the point in a gravitational field. But why the work is ...
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2answers
149 views

How can a magnetic field accelerate particles if it cannot do work?

A varying magnetic field can accelerate charge particles, but it is said that a magnetic field can't do any work so it should not be able to speed up charged particles, right? How is this apparent ...
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2answers
42 views

If I throw a ball horizontally, what are laws, related to Work-Energy concepts, governing that all the situation? [closed]

In a book, A textbook of physics, There was a statement that when we see a motion of body and start to count the laws related to energy-work concepts governing that motion, we at once find ourselves ...
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1answer
55 views

Newton's third law of motion versus Work

Newton third law of motion says that "To every action, there is always an equal and opposite reaction". The vector study tells us that if two vectors are of same nature and equal magnitude but ...
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1answer
42 views

Does $\delta W=pdV$ hold for non-ideal gases

I have that for quasistatic processes, $$ \delta W= \textbf{f}\cdot d\textbf{x} $$ so for a gas $\delta W=pdV$. Does this only hold ideal gases or will it hold for van der waal's gas?
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1answer
22 views

Is Energy said to do work on the body it is stored in?

Assume a boy on top of the hill, his $potential$ $energy=mgh$. He mostarts to move without pedalling the cycle so is that work being done on it due to the conversion of Potential into Kinetic Energy ...
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4answers
61 views

Using formula for work with distance of 0m [duplicate]

Consider this: Wind is pushing a huge rock towards me at with massive force at 2m/s. I push against the rock at equal force so the rock stays still. I am clearly "working" very hard, using a lot of ...
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2answers
31 views

Do transferring energy and applying force to a body imply same?

Do transferring energy and applying force to a body imply same meaning? When we say, "I throw a ball using my pushing force so on the other hand, can I say that I transferred my kinetic energy to the ...
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2answers
71 views

What is the meaning of the negative sign in $W = -\Delta U$?

What is the meaning of the negative sign in $W = -\Delta U$ ? As far as I understand, $W = -\Delta U = -(U_f - U_i) = U_i - U_f$. While $U_i$ is the initial potential energy (before applying the ...
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4answers
45 views

Who is said to do Work, me or the body?

If I subject my force to a body and it is displaced then the work is said to be done. What is that work done by? Is it said to be done by me or that body?
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Why is no work done by magnetic forces in a uniform B and E field (perpendicular to one another)?

Say $B$ points in the $x$ direction, and $E$ points in the $z$ direction. Assuming a charged particle begins at rest at the origin, its motion will be a cycloid that progresses indefinitely in the ...
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How to tell direction of work

I think of direction of work as relative to direction of motion, but I got a question of a parabolic ball throw asking the direction work done by gravity and friction over the entire parabola. Since ...
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2answers
36 views

Work done in lifting chain with nonuniform linear density

I am teaching calculus, and a natural-seeming problem type just occured to me. It would go something like: a 2m chain hangs from the top of a building. Its density at a point h meters from the edge ...
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1answer
25 views

Issue with Work-Change in KE equivalence

First-year physics student, with a pretty basic question. I've seen proofs that Work = Change in Kinetic Energy involving calculus, and they make sense to me, but I'm not sure why the following, much ...
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4answers
813 views

Is the work done walking up an escalator in the same speed and opposite direction of the escalator zero?

Work equals force times distance, but what about walking up an escalator in the same speed and opposite direction of the escalator? In the frame of the ground, the distance is zero so the work must ...
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3answers
64 views

Work power and energy

When you push your bicycle up on an inclined the potential energy of the bicycle and yourself increases. Where does this energy come from?