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

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2answers
325 views

Work done by Friction. Can it be positive or zero?

The work done by frictional force is negative as it opposes the relative motion? Please explain when will the work done by friction be (i) zero (ii) positive ?
1
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2answers
50 views

Volume integral of pressure interpretation

If you have a fluid with with pressure field $p$ what is the physical significance of the the volume integral of the pressure $\int_V p dV$?
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0answers
22 views

Am I exerting force when i am holding something? [duplicate]

So theoretically I found out that I am NOT exerting any force while I am holding something! Like Sir Isaac Newton said F=ma So technically it is true that when I hold something I am resisting it's ...
1
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1answer
107 views

Work Done On Circular Motion

I am trying to find the total work done on a ball, $m=0.8kg$, tied to a rope of r=1.6m length and swung in a vertical circle. I understand the total work done by both the tension in the string and ...
1
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1answer
69 views

Is negative energy(work) less than positive energy(work)?

We cannot talk about magnitudes in case of work, but if someone did (-42 J of work) by stopping a moving object. And if someone did 42 J of work, by pushing something, who did more work? Does it ...
1
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0answers
37 views

Why is the energy lost due to the internal resistance always equal to $(1/2)CV^{2}$ in a simple capacitor battery circuit? [duplicate]

Suppose we have simple circuit in which a battery of EMF $E$ is connected to a capacitor of capacitance $C$. Work done by battery $W_{b}=CV\times V$ and energy stored in capacitor ...
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0answers
31 views

What is exactly gravitational potential energy and explain P.E. $= -GMm/r$? [duplicate]

I was studying gravity and I came to know about $P.E.= -\frac{GMm}{r}$ which is derived by $GMm(\frac{1}{\infty} - \frac{1}{r})$ which the work done by the body to displace it from infinity to $r$. ...
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2answers
403 views

Electric Potential, Work Done by Electric Field & External Force

I did lot of searching but couldn't find any textbook nor any webpage which could clarify my doubt. Maybe my doubt is insanely stupid and I was dumb for not realizing it at the first place. The ...
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2answers
51 views

Am I correct in rejecting this example of No-work force?

I have seen this example in several books. The work done by a porter in carrying a luggage on head while walking on a horizontal force is $0$ as the gravitational force is at $90^0$ with the ...
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2answers
143 views

How can Work and Kinetic Energy have the same units?

If work is Force x Displacement, it would result to N x m, which is Joules. But then, kinetic energy is 0.5mv^2, which is kg x m^2/s^2. Can anybody tell me a way to prove that they have the same ...
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0answers
36 views

work done in observer frame

I had a few questions. 1) Is work done independent of the refrance frame? 2) Suppose a cart-A with rough surface is accelerating with an acceleration a and another cart-B with acceleration b. Now to ...
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4answers
68 views

Must one include friction and gravitational force in the work term?

Example problem: "A sled has an initial velocity up a ramp of 5 m/s, the ramp has an angle of 20 degrees to the horizontal, and the coefficient of dynamic friction between the sled and the plane ...
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2answers
112 views

Conservation of Mechanical Energy Before and After Impact of a Hammer

If a hammer does work by driving a nail into a wooden board, how does the mechanical energy from right before the hammer hits the nail compare to the mechanical energy after the nail has been driven ...
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votes
1answer
98 views

Why is thinking not considered as work? [closed]

While thinking the impulse in our neurons displace and they move in direction of force applied on them. Here the force is applied and impulse moves in direction of force ie it is displaced. Then, why ...
0
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1answer
69 views

How do forces affect work? [closed]

I was doing my homework and I came across the question: Suppose that two objects, each with the same mass, are accelerated from rest to the same velocity. The force that accelerates one object ...
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1answer
49 views

Is it possible to ascend (or descend) an escalator, without consuming any more power produced by the motor of the escalator?

Is it possible to ascend (or descend) an escalator (which ascends with a constant speed), without consuming any more power (energy) produced by the motor of the escalator ? I mean, find a way to walk ...
2
votes
1answer
78 views

Why is friction not dissipative in rolling motion? [duplicate]

We know that non-conservative forces like friction is a dissipative force. But according to my book when a solid cylinder is rolling down a rough inclined plane of inclination angle $\theta$ the ...
1
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1answer
80 views

Question about solving a problem using Newton's Laws and work and energy [closed]

The question is this: Darla pushes a $5.0kg$ crate up a $2.0m$ high $20^o$ frictionless slope by pushing it with a constant horizontal force of $25N$. What is the speed of the crate as it reaches ...
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3answers
344 views

Why is walking up stairs harder than walking normally?

I must admit, I'm pretty new to studying physics and I know this is a simple concept but I'm having difficulty understanding it. I've tried reading the questions here but I just need a little bit of ...
0
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3answers
141 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
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1answer
67 views

Properly deriving the formula for the kinetic energy

I am a physics student and recently attended my first lectures. One thing that strikes me even now was the way the professor derived the formula for the kinetic energy. He started with the (already ...
0
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3answers
90 views

What's the work done by a spring on a block when it moves from extreme to mean position?

I really don't know where am I doing it wrong, but block when it moves towards mean position displacement will be along the force right, so the force acting on block will be $+fxdx$ Integrating we ...
0
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2answers
107 views

Is work a form of energy or means of transfer of energy? [duplicate]

What actually is energy? Is it a property associated with matter or just a number? By doing work are we changing the energy of the body or converting one form of energy into other which is already ...
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2answers
43 views

Phsyics Energy Problem + Concept

A simple problem really. Part 1 Suppose a ball ($20. ~kg$) was shot straight up with an initial velocity of $+50~m/s$. a. Assuming that all of the ball's initial $E_k$ was transformed into ...
2
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2answers
56 views

I have trouble understanding work

I am just starting out in physics. I study in germany, so excuse me if I get some terms wrong. I am trying to understand why 'Work = Force * Way' and I think I just have some trouble imagining what ...
0
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1answer
58 views

A question about thermodynamic reversible process [closed]

I am a new learner of thermodynamics, and I have a question in my assignment: Show that $W$ and $Q$ for an arbitraty mechanically reversible nonflow process are given by: $$W=\int VdP - ...
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1answer
43 views

Calculation of Work

Typically I see problems laid out along these lines. If you are lifting a 100 kg weight 1 meter how much work do you do? Work = Force * Distance Work = (100 kg) (9.8 m/s^2) * 1 m = 980 J But it ...
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2answers
55 views

Finding the work done to fill the tank by pumping water over the edge? [closed]

I am really confused on how to approach the following question and how to set it up. So the question is: An open tank has the shape of a frustrum of a right circular cone. The tank is ...
0
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2answers
48 views

Where does the energy required to speed the object in this question come from if the object actually slows down from another perspective?

I was thinking about mechanics and energy and stumped myself with this scenario I made up: Suppose you are in a room and you are motionless. In the same room, a 1 Kg ball is moving to your right with ...
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votes
1answer
57 views

Why is a satellite's GPE negative? [duplicate]

Okay, so the formula for Gravitational Potential Energy (GPE) of satellites is: $$ U=-GmM/d$$ Mass and distance can't be negative, and $G$ is constant that is not negative. Why is a satellite's GPE ...
0
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2answers
113 views

The work done by a spring over a specific distance

I cannot seem to find the answer for my question. I know that the formula for work is $W = FD$. Given a mass that is attached to unstretched spring and is pushed by some force to stretch the spring, ...
0
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3answers
231 views

Why does the work-energy theorem need to include internal forces?

Can anyone kindly explain me why work energy theorem must also include internal forces? The proof of work energy theorem is derived from Newton's laws of motion, but Newton's laws of motion don't ...
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1answer
59 views

Work done should be positive but it is coming out to be negative? [closed]

I have described a question in which this problem arises in the image below:
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2answers
111 views

Can a glider maintain a constant forward velocity component?

I have a puzzle which asks me to consider a (engineless) glider descending at a constant rate and flying at a constant forward velocity (in still air). The question asks how to derive sink rate, $v_s ...
0
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1answer
32 views

Work done when applying an electric field?

On these example questions from MIT in the solution to 4.1 they write the work done by applying the electric field to be: $$W=V_0 \int \vec E \cdot d \vec D$$ Where does this equation come from and ...
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1answer
81 views

Work done by friction opposing a force at an angle

Let's imagine there's a block of mass m sitting on a rough surface with a kinetic friction coefficient $\mu$. It's being pulled with a constant force $A$ at $h$ degrees above the horizontal and is ...
4
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3answers
2k views

Where does the energy go in a rocket when no work is done?

While playing Kerbal Space Program, I wondered where my chemical energy would go when fired at 90° to the motion. It would do no work on the rocket, but all that energy has to go somewhere, right? ...
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1answer
39 views

Heat, Work and Internal energy in closed systems

This has been troubling me for a while now. I know that the performed work equals $P\Delta V$ for isobaric systems and I know that in isochoric systems no work is done, but how do I find the heat $Q$? ...
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1answer
80 views

Work done by gravitational force!

Suppose a ball is $10m$ high from the ground. It will have $E_p = 10mg$. Now, if the ball falls freely then we know $E_k$ will be $0.5mv^2 = E_p$. But it is said that the work done by a force will ...
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2answers
151 views

Work done against gravity comes out positive

Given two points in 3-space, $A = (9, 1, 5)$ and $B=(2,8,7)$, the work done by the gravitational field $\bf{F}$ when an object is moved from point $A$ to point $B$ comes out positive, even though it ...
3
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3answers
904 views

Problem in understanding the Proof of $PV^{\gamma}$ =constant in thermodynamics

I have looked at the proof of this relation $PV^\gamma = C$; (where $P$ is pressure and $V$ is volume) in quite some places but I am not able to understand the logic behind the third step. In ...
3
votes
4answers
341 views

Can infinite work be done?

Wikipedia defines work as follows. In physics, a force is said to do work if, when acting on a body, there is a displacement of the point of application in the direction of the force. Also work ...
1
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1answer
271 views

Electric field for concentric spheres

I have a couple clarifying questions: (A) in $E=kq/r^2$ for the area between a sphere inside another spherical shell, the sphere inside is considered a point charge. However, the sphere inside has a ...
1
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1answer
136 views

How are the watt-second, the newton-meter and the joule different?

The joule is $\mathrm{kg\,\ m^2/s^2}$ right? The watt-second is $\mathrm{J/s} \times \mathrm{s}$ thus $\mathrm{J}$. The newton-meter is $\mathrm{kg \,\ m/s^2} \times \mathrm{m}$ thus $\mathrm{kg \,\ ...
0
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2answers
487 views

Change in internal energy is 0 in isothermal process

I am having trouble understanding why in an isothermal process, the change in internal energy is zero. I know that $\Delta U$ or $\Delta E=q+w$, and so in isothermal process $q=0$. But how does one ...
0
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1answer
52 views

Work and energy question

An athlete picks up a $20.0\,\mathrm{kg}$ sandbag from the ground and throws t straight up in the air. It leaves her hands $1.50\,\mathrm{m}$ above the ground and reaches a height of ...
0
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2answers
87 views

Why isn't the work minus the potential energy when bringing a charge in from infinity?

This is an example in my physics textbook, and there is just one step that I don't understand. Two point charges are located on the x-axis, $q_1 = -e$ at $x = 0$ and $q_2 = +e$ at $x=a$. Find ...
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2answers
132 views

Can I define the term energy in terms of work?

Recently, I'm doing my personal task which is to formalize every definition and concept in physics, by means of formal language and of course with intuitional notes. Because I found myself that the ...
0
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3answers
128 views

Work done by a constant vector field is 0?

We know that $$\oint \boldsymbol{F}\cdot d\boldsymbol{r}= \iint (\nabla \times \boldsymbol{F})\cdot d\boldsymbol{s}.$$ Now if $\boldsymbol{F}$ is a constant vector, then $\nabla \times ...
1
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1answer
357 views

Is work energy theorem $W=\Delta K$ or $W=\Delta E$?

I know that work is the change in kinetic energy. I saw on an equation sheet that work is equal to the change in total energy. Is this true? If so, how?