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

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16 views

COP and input work in a refrigerator

Where can i find a COP and input work requierd in a standard modern refrigerator? I need a sample refrigerator, so that I can calculate the heat disposed to the surrounding and use that to design an ...
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1answer
16 views

a question on work and kinetic energy [on hold]

A bullet has a mass of 0.02kg and is moving with a speed of 10m/s. It can penetrate 10cm of a given target before coming to rest. If the same target is only 6cm thick, what will be the speed and ...
2
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0answers
36 views

Work by Gravity using Tensors [on hold]

Now I'm familiar with the various methods for deriving work done by gravity, but I noticed a few things about the situation, and wanted to see if I could properly apply a tensor treatment to the ...
1
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3answers
172 views

Where Potential increase gets it's energy from?

Imagine there are two particles: A,B; of which, we observe A to be stationary, while B is moving towards A at velocity v. A,B has same mass; and they are charged both positive. B has a potential wrt ...
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2answers
32 views

Conservation of energy in vertical circular motion

Books usually use conservation of energy to solve problems in vertical circular motion. But, principle of conservation of energy for one particle is, If all the $n$ forces $\vec F_i ...
2
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2answers
51 views

Why dont you take derivative of force in definition of power ? P=F.v

The derivative of work is $\bf F\cdot v .$ $$P(t)= \frac{\mathrm dW}{\mathrm dt}= \mathbf{F\cdot v}=-\frac{\mathrm dU}{\mathrm dt}\;.$$ But why not $$(\mathrm d(\mathbf F)/\mathrm dx)\cdot \mathbf x ...
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2answers
41 views

Work-Energy Problem

A wire, which passes through the hole in a small bead, is bent in the form of quarter of a circle. The wire is fixed vertically on ground as shown in the figure. The bead is released from near the top ...
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0answers
17 views

Which ball travels further, one that is thrown up a frictionless ramp or one that is thrown in the air? [on hold]

They are thrown at the same angle, and their masses are equal. Please explain using basic physics, if you can. We only learned: Kinetic, potential energy Work Velocity
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1answer
64 views

Does this count as a proper derivation of the formula for work and kinetic energy? [on hold]

$v_{av}$ = average velocity, $d$= distance, $a$ = acceleration, $m$ = mass Given: $$v_{av}*t=d$$ $$t=\frac{v_f-v_i}{a}$$ $$v_{av}=\frac{v_f+v_i}{2}$$ Then: $$\frac{v_f+v_i}{2}*\frac{v_f-v_i}{a}=d$$ ...
0
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4answers
74 views

When writing a differential equation, when do you take $+\text{d}x$ and when do you take $-\text{d}x$?

When writing a differential equation I'm confused as to when to write $+\text{d}x$ a and when to write $-\text{d}x$ a where $x$ represents some quantity. For example, I wanted to derive the equation ...
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1answer
41 views

Why the force acting on a particle is the negative gradient of a scalar potential? [closed]

For conservative forces we can proof that it is a gradient of a scalar potential, but why we use the negative sign? In every book I searched, it said that it is like an agreement between physicists, ...
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0answers
21 views

Work + heat absorbed in a thermodynamic process

The question describes a simple isobaric closed cycle. The temperature is on the y-axis and volume on the other. There are 4 states. The question asks: ''Find the work done on the gas in the cycle and ...
1
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2answers
43 views

Question about Kinetic Energy and Force acting on a body

Below is the graph of a body that rests on a friction-less flat surface. On this body force F is applied and it's value is being depicted in the graph below. We can see that the body moves from point ...
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0answers
20 views

Will Energy and Work equal to each other between two closed systems linked by one shareable object?

Two closed systems are linked to each other. Both use same object. In one of this closed systems was spent energy to change physical property of shareable object. After this object transformation, ...
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2answers
78 views

Confusion with $F=-\nabla V$, $F$ conservative

I am rather confused by the relationship $F=-\nabla V$. If a pen drops from a height it loses potential energy so $\nabla V$ is negative. From the above equation this means that the gravitational ...
1
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0answers
23 views

Magnetic Forces and Junkyard Magnets: What's Going On? [duplicate]

In my electromagnetic theory class, I learned that magnetic forces do no work. This is easy to see when observing a cyclotron; the speed never changes, so the kinetic energy never changes and ...
0
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2answers
81 views

When I move while holding a book, why is work done zero?

Now this question has many answers all over the internet, but this site gives me the power to pose my doubts in front of you all. Let's get straight to it: Suppose I move on a road while holding a ...
2
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0answers
41 views

Energy expressions [closed]

How did people come up with various expressions for energy? By this I mean the expression or formulas for kinetic energy, gravitational potential energy etc. and the intuitive guiding principles to ...
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3answers
56 views

Is there any other way to describe work done instead of saying the force applied to move an object through a distance?

I was reading about energy, and I got to know that energy is the ability to do work. Then I read about work, and I found that almost everywhere, resources say that when an object applies force to move ...
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3answers
69 views

If I walk forward and stop was there work done?

If I'm on a flat surface and I start walking and go to a constant velocity, then I slow myself back down to a stop, was there work done? I would think the answer is no because $work = force * ...
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1answer
52 views

Gravitational Potential Energy misunderstandings [closed]

I'm really confused by the derivation of Gravitational Potiential Energy. I took a screenshot of the wikipedia entry below. My major confusion lies in: 1. The use of the position vector r in the ...
2
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3answers
147 views

The float on a frozen lake

We have a bit of a debate going on at work. If a basketball (or any round float - let's assume one firm enough to not change size with temperature) was floating on a lake, and overnight the lake ...
0
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1answer
36 views

Thermal Energy in a pV diagram

I'm studying for an exam in thermodynamics and therefore going through old exams, but I am stuck on one assignment. One kilomole of ideal monoatomic gas under standard conditions is processed ...
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2answers
48 views

Sliding along a circular hoop: work done by friction

Assume a point object of mass $m$ slides along a hoop of radius $R$, starting from a position which makes 90 degrees with the line of radius connecting the center and the ground. Let the ...
2
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1answer
51 views

The source of work by gravity force [duplicate]

I learn that any work needs a source of energy, the work of gravity force (like keeping the Moon in the orbit by the Earth gravity force) comes from where? Can we find any mass reduction (transform ...
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0answers
23 views

Sign of elastic potential from a spring [closed]

When writing the Lagrangian of a problem, how do I determine the sign of an elastic potential from a spring?
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2answers
47 views

Work done by pressure

The problem is How much work is done by pressure in forcing $1.4 m^3$ of water through a pipe having an internal diameter of $13 mm$ if the difference in pressure at the two ends of the pipe ...
0
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3answers
58 views

Why is there potential Energy due to lifting an object or moving when it's attached to a spring while the net work is zero?

Consider that you lift an object a height h vertically, if the body happens to move with uniform velocity this means that net force acting on it is zero. The same is true for a body attached to a ...
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2answers
44 views

Work done by a spring

I've done enough research before asking this question. The work done by a spring is defined as $$W_\mathrm{spring}=\left|\frac{1}{2}kx^2\right|$$ Where $ k$ is the spring constant and $x$ is the ...
2
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1answer
44 views

Is the integral of $dK$ equal the work done?

$$\frac{dK}{dt} = \frac{d}{dt} (1/2 mv^2) = mv \frac{dv}{dt} = F\frac{dx}{dt}$$ $$\implies dK = F. dr$$ Also, work is defined as $W = \int F. dr$. So does this imply integral $dK = W$?
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29 views

The relation between work and time

Work equals the force acting on an object times the distance that object moves. But I am a bit confused about the definition of the distance. is it the distance the object moves under the effect of ...
1
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1answer
47 views

Confusion regarding the sign of the work of a force

The work of a force is given by the following line integral: \begin{equation} W=\int_{A}^{B}\vec{F}\cdot \vec{dl} \end{equation} So the work that is needed for an electric particle to be moved in an ...
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2answers
94 views

Why are gravity and spring-force conservative forces?

I know that the amount of work does not depend on the followed path but on the position when speaking about conservative forces. But could someone please prove/explain why exactly those two are ...
0
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3answers
74 views

Why can't we define a potential energy for a non-conservative force? [closed]

We could define potential energies for non-conservative forces too and then we could conserve it with kinetic and potential energy as we know it. But no one does that. Why is this? Please explain. Any ...
2
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1answer
45 views

Work done by a body

This is a fundamental doubt Can we use the formula W is equal to F*D only when the body is accelerated? For example if the acceleration does not remain constant can we use it?
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3answers
394 views

What does it mean to say work is path-independent when pushing an object in different directions?

If I apply a straight upward(perpendicular to ground) force against gravity of $5\ \mathrm{N}$ and lift an object "A" 10 meters, then the work done is: $$ W = F \times S = 5\ \mathrm{N} \times 10\ ...
0
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2answers
63 views

Why does the gravitational potential energy decreases as balloon filled with hydrogen ascends up?

As body ascends height increases from the formula $mgh$ the increasing height should increase magnitude of P.E. but some say we should take height negative as it is going up against gravity.
2
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2answers
53 views

What is a qualitative description of energy? [duplicate]

In elementary physics courses one is taught that energy is a measure of an object's ability to do work (this in itself seems a little flaky as how does one then define exactly what "work" is, other ...
33
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4answers
4k views

What is the energy source if a tall water tank is used to transfer floating objects upwards instead of cables with motors?

Suppose I want to transport some logs from the ground to the roof of a tower. Originally I can use a lift, or some cables, or even move the logs upwards manually; then the energy is converted to the ...
1
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0answers
10 views

Solving question from a energy perspective [closed]

Im having some trouble with a question i was given for homework. Ive already solved it from a motion perspective but now i need to solve it from a energy perspective. The question states that from a ...
3
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3answers
149 views

Work done changes between reference frames?

(This is not homework; a friend shared with me this puzzler and neither of us can figure it out.) Suppose you are in a plane traveling at velocity $v_1$ relative to the ground. The flight attendent ...
-4
votes
2answers
95 views

Dilemma About Energy : Can You EXPLAIN? [closed]

PROBLEM 1 : A 2.14 kg block is dropped from a height of 43.6 cm onto a spring of force constant k = 18.6 N/cm as shown in fig:12-19.find the maximum distance the spring will be compressed. solution ...
0
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0answers
17 views

Work power and energy question, circular path [duplicate]

Suppose when someone travel in a circular path and covers 2 pie r distance. Is he done some work or not.(here r is radius of circle). work done is only force times displacement or force times distance ...
1
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4answers
77 views

Question on work power and energy [duplicate]

A person holds a bundle of grass over his head for 30 minutes and gets tired. Has he done some work or not please explain me?
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2answers
33 views

Tension at topmost point of a vertical circle

I read that for a body to move in a vertical circle, the minimum tension needed is 0 at the topmost point. Can someone explain to me what it means to have positive or negative tension on top. I'm not ...
0
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1answer
40 views

Energy/entropy in transport of molecules across cell membranes

I'm asking a "Maxwell's Demon" question. I've read statements that sorting molecules and sending them to one side or the other of a barrier requires work, but none of these statements have explained ...
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1answer
24 views

How is work constant when I raise a body to a height?

My friend asked me- Imagine that we pull up a pen which is initially at the ground slowly upwards.At a certain point we see that its total energy is due to its P.E.So,how can we say total energy ...
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1answer
22 views

Net work performed on projectile

If a ball is thrown into the air, we may assume it has an initial positive kinetic energy $E_k$, and its gravitational potential energy $U_g$ is 0. Once it reaches its apex, $E_k=0$ and ...
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1answer
69 views

Confusion about the definition of Work

I am trying to make sense of the meaning of the definition of work. The original definition of work was also known as "the weight lifted through a height." I was hoping that our mathematical ...
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0answers
23 views

In terms of work, what happens to a negatively charged particle circling around a positively charged rod?

Picture a positively charged glass rod from its end so that if you were to draw it on paper, it would appear as a circle. Now, suppose a negatively charged particle moves in a circular arc, on the ...