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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.

2
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2answers
24 views

Friction and Work in Inertial Reference Frames

Say a train is moving in the positive $x$-direction at 100 meters per second with respect to the ground frame. Now let's say someone is pushing a large box in one of the cars of that train in the ...
0
votes
1answer
28 views

Work done on box

I am having a hard time grasping this. W = Fd = mad, and given v vs t graph, the area under the curve will give us d. When the velocity graph draws a horizontal line, a=0. Thus I thought that A = C ...
0
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1answer
44 views

Confusion in work done in moving charge to infinity from center of conductor

A point charge $q$ is at center of spherical conducting shell of inner radius $a$ and outer radius $b$. Find work done in moving charge to infinity. The answer (given in book) is: $$W = \frac{q^2}{8\...
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0answers
29 views

Work done on a non-rigid object

I know it is possible to calculate the work done on the center of mass in any given system, and hence, its increase in translational energy. For a non-rigid object, however, can we still compute its ...
0
votes
1answer
55 views

Calculating power with force as a function of time [on hold]

While doing an AP question in Physics C today I answered the question differently from the professor but I'm not sure what part of my reasoning is incorrect. The question gives the position of a block ...
0
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0answers
13 views

What's the spring constant when a block of mass $m$ is suddenly released from a spring of negligible mass? [on hold]

Suppose, a block of mass 10 kg is attached to a massless spring. After the block is released, it oscillates. The lowest point that it reaches is 5m. What's the spring constant? My approach: The force ...
2
votes
2answers
84 views

What is function of force $F$ and work $W$?

I know that : Position $$r:\mathbb{R} \to\mathbb{R^3} \ \ \ \ \ ; \overrightarrow{r}(t)$$ Velocity $$v :\mathbb{R} \to\mathbb{R^3} \ \ \ \ \ ; \overrightarrow{v}(t)$$ Acceleration $$a:\mathbb{R} \...
-1
votes
1answer
60 views

Work done by stationary floor

When a rod falls on floor in such a way that the rod starts rotating. The work done by floor is zero as floor is not moving. But still, rotational kinetic energy is changing. Is it due to the fact ...
0
votes
1answer
50 views

Why is the work done the same in this case? [on hold]

The formula for work is $W= Fd \cos \theta$. A body, which is pivoted at point P, and wherein force is applied at point F1 first and then at point F2, rotates from position 1 upto position 2 in both ...
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vote
3answers
53 views

Converting potential energy to kinetic energy

I know how potential and kinetic energy interrelate when you drop anything. But is it a general understanding in the community that a change in potential energy is always kinetic energy? I am ...
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0answers
16 views

Change of Direction work [closed]

If a car is moving at 5 m/s in the positive direction before and now it is moving 5 m/s in the negative direction is work done?
1
vote
4answers
120 views

Work done but no change in velocity

I’m taking an introductory course in thermodynamics right now and I have learned that in a quasi static process, one way to increase internal energy is to do work on a system or supply heat to it. But ...
1
vote
2answers
90 views

Positive work along path [on hold]

Consider I have a simple formula for the work along some path (in 1 dimension): $$W~=~\int_{x_0}^{x_1}\vec{F}\cdot d\vec{x}.$$ If I now move from left to right ($x_1 > x_0$) along the axis (...
-2
votes
0answers
26 views

Newtonian Mechanics- Method of Work [closed]

Q230: The question asks to find speed with which point mass M hits the wall when system is set free. I don't understand- It somehow doesn't fit in my intuition how mass M could hit the wall? Can ...
1
vote
2answers
100 views

Does gravity matter when calculating work done horizontally?

My teacher gave the following question: A 212lb running back can complete the 40yd dash in 4.53s. What time would a 198lb running back have to post in order to be more powerful? My teacher says that ...
1
vote
2answers
43 views

Why is the net work of a falling object impacting the ground zero?

In my physics textbook, I found the following problem: "A 2,100 kg pile driver is used to drive a steel I-Beam into the ground. The pile driver falls 5.00m before coming into contact with the top of ...
0
votes
1answer
33 views

What's the work done in raising a rod from the lying position by using the torque?

This problem can be solved using the centre of mass. We can just calculate the change of the potential energy and that'd be the work done. That way, $W = MgL/2$ (since the cm is at $L/2$). I ...
0
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3answers
37 views

Sign of work in adiabatic expansion

I know that in an adiabatic expansion, $W = -U.$ My question is, is the work positive or negative? I'm confused on the difference between work done "by" the system and work done "on" the system.
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0answers
24 views

External Work vs. Center of Mass Work

I've read through the answers to similar questions but none of them have cleared my doubts: My physics textbook states that the total external work on a system is equal to the change in energy and ...
1
vote
0answers
30 views

Trying to get one step closer to the understanding of free energies $F$ and $G$

I find it quite hard to get a good grasp of the notions of Helmoltz and Gibbs free energy, because they can be introduced in so many different ways, and embody so many different ideas at once... Here,...
3
votes
1answer
289 views

Is it wrong to imagine the gravitational potential of a system based on the center of mass?

I was practising some questions until I stumbled upon a question. A chain of length $l$ and mass $m$ lies on the surface of a smooth sphere of radius $R>l$ with one end tied to the top of the ...
0
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0answers
26 views

Doubt regarding work done in separating capacitor plates [duplicate]

Suppose there is a parallel plate capacitor with distance between plates $d$ and it is charged to a potential difference $V$ and then charging battery is disconnected. Then the plates are further ...
0
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0answers
39 views

entropy transfer v. work transfer

Are there any work transfer mechanisms that cannot transfer entropy and if so why? What are the general theoretical limitations on entropy transfer from one system to another? By system I do not just ...
0
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2answers
39 views

Work done by electric field in a wire

Work done by electric field in moving a unit charge is the potential drop. In wires voltage (potential drop) is given by ohms law. Can somebody explain to me why work done by electric field can not be ...
12
votes
4answers
2k views

Work done by a gas

In the expression for work done by a gas, $$W=\int P \,\mathrm{d}V,$$ aren't we supposed to use internal pressure? Moreover work done by gas is the work done by the force exerted by the gas, but ...
0
votes
1answer
31 views

Why is Kinetic Energy in Energy-Distance graph linear, but parabolic in Energy-Time?

Specifically, the projectile (falling off a table) problem. The graph of the Energy-Distance is linear, but I don't understand why. Isn't $KE = (1/2)mv^2$?
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4answers
95 views

Why is Work equal to Force * distance?

I totally get the mathematical part, but I cannot imagine how this works. I apply a force to a ball. Why does the distance over which it moves matter to me? Sure, if I calculate the kinetic Energy of ...
-1
votes
3answers
68 views

Energy of an object

When an object goes up we say that it gained potential energy but it is doing positive work on the earth so it should lose energy.Please correct me.
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5answers
3k views

Why do we have to dump the extra entropy created in a heat engine?

In his introduction to thermophysics, Daniel Schroeder writes the following about the process in a heat engine: Only part of the energy absorbed as heat can be converted to work. The reason is, ...
1
vote
1answer
27 views

Problem regarding finding work done

This problem is given in my physics book. How much work will be done if anyone wants to stack up 12 bricks? Given that each brick is $10 cm$ high and each brick's mass is $2 kg$. ($g=9.8$) Now in ...
2
votes
1answer
60 views

On Joule's free expansion experiment

While reading through an introductory textbook in Thermodynamics, I've come across a series of arguments that seem somewhat arbitrary/vague, on which I'd like some clarification. To begin with, the ...
0
votes
1answer
40 views

If a box is carried 2 flights of stairs to an attic, is more work done than opposed to go straight up with a ladder? [duplicate]

The box has the same weight. I think that the stairs does more work because it travels a further distance as it is a less direct path opposed to going straight up.
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votes
1answer
45 views

Calculate top speed of vehicle [closed]

I'm trying to figure out the top speed of a vehicle and the time it would take to get there. Information about the vehicle: Mass $m = 200 \, \mathrm{kg} ;$ Engine power $= 1000 \, \mathrm{W} ;$ ...
9
votes
6answers
693 views

Definition of inner product as in the case of work

According to the mathematical definition of "vectors", vectors are simply the elements of a set $V$ which forms a vector space structure $(V,F,+,*)$. The definition of inner product states that it is ...
2
votes
1answer
55 views

Melting ice inside water by increasing pressure

An ice cube is floating in water inside a container and the system is in thermal equilibrium. And let say we somehow immerse the ice cube slowly into deeper region inside the container (we may pull a ...
1
vote
2answers
71 views

Can't understand energy conservation in simple thermodynamics example

SITUATION Consider a very big cylinder with a mobile piston in the middle separating two sections (A and B) filled with gas. Both the cylinder walls and the piston are adiabatic, so there is no ...
0
votes
1answer
41 views

Regarding the equivalence of expressions for the change in internal energy of a system when the process is not quasi-static

It is well-established that some authors prefer expressing the change in internal energy of a thermodynamic system in terms of the work done ON the system and others will express it in terms of the ...
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0answers
31 views

Would it be appropriate to say that in presence of Non-Conservative Forces, the Entropy of System Always Increases?

Would it be appropriate to say that in Presence of Non Conservative Forces the Entropy of a system would always increase? Can we relate Non-Conservative Forces and Entropy in some way? I intuitively ...
10
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5answers
752 views

Paradox in the definition of work [duplicate]

I'm trying to understand the Oberth effect and came across this paragraph that seems crazy to me: when the rocket moves, its thrust acts through the distance it moves. Force multiplied by distance ...
0
votes
1answer
50 views

Finding out heat generated in presence of variable force when minimum work done [closed]

Ques: A portion of a floor in a lab is made friction less.A homogeneous bar of length l= 1.0m placed on the friction less portion perpendicular its boundary is being dragged by pulling it with the ...
0
votes
2answers
30 views

Is the work in line integrals equivalent to the work as an area under the curve?

A little explanation is needed here. Let me use two dimensions. In a line integral a curve is given and usually one parametrizes yet another curve and then substitutes this into the original equation ...
-1
votes
3answers
75 views

Can someone explain this equation more clearly: $\Delta E_{Total}=\Delta K + \Delta U = W_{External}$

I asked my Physics teacher and he explained it to me, but I am still confused on how to use it. \begin{equation} \Delta E_{Total}=\Delta K + \Delta U = W_{External} \end{equation} I think it's the "...
1
vote
2answers
26 views

Displacement using work energy principle

How do you use the work energy principle to find the displacement of an object. With of course the mass, speed and friction forces given?
1
vote
2answers
55 views

Why, when calculating work done when a person climbs stairs, the distance is the height of the stairs but not the distance the person travels?

I was thinking, since Work Done = Force * Distance moved in the direction of the force , the distance moved in the direction of the force would be the distance of the slanted stairs instead of the ...
0
votes
0answers
16 views

Can a car accelerate on a frictionless surface? [duplicate]

i have string of related questions. i know that the internal forces cannot result in acceleration of a body and so in daily life, car engine applies force to rotate wheels that produce friction force (...
0
votes
2answers
69 views

Does stirring a liquid add heat $Q$ to a system? [closed]

I was given a question, "A thermos bottle containing milk is shaken vigorously. Consider the milk as the system. (a) Will the temperature rise as a result of the shaking? (b) has heat ...
1
vote
2answers
68 views

Work done by friction on a body which is rolling on an inclined plane [closed]

Why is the work done by friction zero during translational motion but nonzero when the body is rolling on an inclined plane?
0
votes
1answer
59 views

When we push on a wall, why isn't there any work done? [duplicate]

I have seen a similar question on the site, but that was kind of different in its essence — it was aimed at asking the solution of a particular problem, while I am having trouble conceptualizing the ...
-2
votes
1answer
57 views

Uniform Circular Motion and Work [closed]

I was usually told that in a uniform circular motion the work is 0 because the force is every instant perpendicular to the displacement. However, studying the motion i noticed that there is a force ...
0
votes
1answer
31 views

Pumping fluid out of a tank: how does intake location affect work?

I was working a calculus II problem on the board, teaching how to solve the fluid pumping problems. I drew a tube from the top of the container to the bottom, and a student asked about how that ...