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
191 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
108 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
votes
1answer
71 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?
5
votes
3answers
537 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
votes
2answers
97 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
votes
2answers
74 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 ...
34
votes
4answers
5k 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 ...
3
votes
2answers
168 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 ...
-5
votes
2answers
125 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
votes
0answers
18 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
vote
4answers
127 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?
1
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2answers
49 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
votes
1answer
121 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 ...
0
votes
1answer
30 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 ...
0
votes
1answer
24 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 $U_g=E_k(...
-1
votes
1answer
73 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 ...
0
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0answers
37 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 ...
-1
votes
2answers
389 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
vote
2answers
51 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 $\int_V p dV$?
1
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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
vote
1answer
113 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
vote
1answer
73 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 $=\frac{1}{2}CV^{2}$...
1
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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 $r$. ...
1
vote
2answers
497 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 ...
0
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2answers
52 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 ...
0
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2answers
161 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 units?...
1
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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 ...
0
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4answers
70 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 ...
0
votes
2answers
116 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 ...
-2
votes
1answer
99 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
votes
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 ...
0
votes
1answer
50 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
81 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
vote
1answer
86 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 ...
0
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3answers
422 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
votes
3answers
152 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
votes
1answer
71 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
votes
3answers
100 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
votes
2answers
119 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 ...
0
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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
votes
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
votes
1answer
61 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 - \Delta(...
0
votes
1answer
45 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 ...
0
votes
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 $4\:\mathrm{...
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 ...
-1
votes
1answer
60 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
votes
2answers
116 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
votes
3answers
240 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 ...
-1
votes
1answer
63 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: