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

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1answer
90 views

Determination of displacement value in work formula

A net force will always create displacement which approaches infinity if left undisturbed. So how to fix a value of displacement in work formula? Isn't a mention time interval necessary? Or do we ...
0
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1answer
102 views

Starcraft II: Estimate how much air a viper would have to move to abduct an ultralisk [closed]

This is a physics question about an in-game world scenario. In Starcraft II, there is a flying unit called "viper". It has the ability to abduct huge, massive enemy units - while remaining stationary ...
2
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2answers
151 views

Entropy $dQ=TdS$ and Work $dW = -pdV$ conditions?

What are the conditions in order for the equations: Entropy $dQ = TdS$ and Work $dW = -p dV$ to work? I think for $dQ = T dS$, it must be a reversible process? But for $dW = -p dV$, shouldn't it ...
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3answers
91 views

Is there work done when two current carrying wires are attracted?

When a current carrying wire attracts(or repels) another wire, the wire moves under the action of a force. Also, it is obvious that the work done is due to force of "magnetic field" on "moving ...
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4answers
72 views

The work done by running in a rectangle

This may be quite off-topic but please help me. Is there any work done when I run in a rectangle? I thought that the answer should be no. But my teacher says that we should calculate each side ...
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3answers
6k views

Why work is a scalar and not a vector?

Work (in physics) is a scalar but why? and why not a vector?
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1answer
36 views

Applying conservation of energy to any system?

How would the conservation of energy be applied in any system? Can we always be certain that every system will always obey COE? How can we be certain without measuring the system? Input & Output? ...
11
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6answers
2k views

Why is there a $\frac 1 2$ in $\frac 1 2 mv^2$?

For elastic collisions of n particles, we know that momentum in the three orthogonal directions are independently conserved:$$ \frac{d}{dt}\sum\limits_i^n m_iv_{ij} =0,\quad j=1,2,3$$ From this, it ...
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2answers
152 views

Is there a mistake in this example in my mechanics textbook?

This is a worked example in my mechanics book: But I think this worked example is wrong. In the 6th line. shouldn't $X=4R$ as the expression for distance above the surface is $(X-R)$ and when the ...
2
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1answer
23 views

Minimum Power Required

Here is a question, I found two methods to solve it, differing in the answers and I'm not sure why a method is incorrect. Question: A fire hose of cross section area ...
3
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4answers
3k views

What is $vdp$ work and when do I use it?

I am a little confused, from the first law of thermodynamics (energy conservation) $$\Delta E = \delta Q - \delta W $$ If the amount of work done is a volume expansion of a gas in, say a piston ...
4
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2answers
90 views

What exactly is ''electric energy''?

If the two fundamental types of energy are kinetic and potential energy, is electric energy simply the kinetic energy of charge carriers? Also, is the statement "A cell converts chemical potential ...
1
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1answer
83 views

Confusion with curl of Lorentz magnetic force

Since the magnetic force is a no work force, $dW=\vec F\cdot d\vec r=0$ for $\vec F(\vec r)=q(\vec v(\vec r) \times \vec B(\vec r))$, therefore $\oint \vec F \cdot d\vec r=0$ by Stoke's theorem. ...
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votes
3answers
770 views

Number of planks required to stop the bullet [closed]

A bullet looses (1/n)th of its velocity passing through one plank. The number of such planks that are required to stop the bullet can be? Logically, to me the answer seems to be infinity, as always a ...
2
votes
1answer
37 views

Work done or not in this case?

I have a very simple question. A motorboat directed upstream is seen to be at rest from the bank of a river. Is the engine doing any work? Is it right to say that since it is not causing any ...
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2answers
197 views

Why do two equal-and-opposing forces each do work on a moving object but not on a stationary object?

Consider a point-mass $m$ having constant velocity but undergoing influence from two forces, $F_1$, $F_2$, having equal magnitude but opposite directions. Because the forces' magnitudes are equal, I ...
-3
votes
1answer
34 views

Work done from force-extension graph [closed]

The answer is C, but I got B... F at 3cm = 10, F at 6cm = 20 $W=F\cdot s$ $(20-10)\times 3=30$ I must have made a mistake or stupid assumption then, how am I meant to get 45 N cm?
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votes
7answers
912 views

In calculating work done by a constant force over a constant distance, why doesn't the subject's initial velocity matter?

Assume a point-mass $m$ is travelling in a straight line, and a force $F$ will act on $m$ (in the same direction as $m$'s velocity) over a constant distance $d$; why doesn't $m$'s velocity matter to ...
1
vote
1answer
50 views

Work done (by gravity) on paired blocks [closed]

Why does gravity do more work on the block going down? The total work done (by gravity) on the $8kg$ block is more than the work done (by gravity) on the lighter block. How?
0
votes
1answer
85 views

The formula used to calculate electrical potential energy

Sorry for the ugly picture but it makes my question more understandable. The $\Delta V$ from $A$ to $B$ is calculated by$$\int_A^B E \, \mathrm{d}r$$ where $r$ is the distance between $A$ and $B$. ...
0
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2answers
46 views

The context of definition of work [duplicate]

It is unclear whether the work is defined considering opposite force on the same body or in ideal case where there is a single force acting on a body.If we consider ideal case where only a single ...
0
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3answers
40 views

Energy, time and force

Consider force $F$ acting on a body of mass 1000kg and the displacement be $s$. So energy required to do so is $F$x $s$. Now consider the same force causing same displacement on body of mass 1kg. ...
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1answer
53 views

What is Work? What does the quantity suggest intuitively? [duplicate]

The mathematical formula for work says that work is force into displacement, but what is the philosophy behind it? I mean what does the quantity suggest?
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0answers
27 views

Restrained expansion of a piston/cylinder

Suppose an ideal gas in a piston cylinder has some initial pressure $p_1$, volume $V_1$, and temperature $T_1$. A pin, which holds the piston in place, is suddenly removed, and the gas quickly ...
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2answers
302 views

Measuring work done by gravity over non-constant gravitational acceleration

A question from an example from a MIT Classical Mechanics Lecture on Work. Here's the given definition for gravitational potential energy (~32:00): "The ...
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2answers
94 views

Work in Newtonian Mechanics and Thermodynamics

Well, is the basic difference between the work that we learn in Mechanics and that in Thermodynamics? This is because in Mechanics, whenever work of magnitude $W$ is done on a system $S$, then the ...
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1answer
73 views

Line Integral Parameterization

In math, I was taught to parameterize a scalar/vector line integral. In physics, I remember doing problems where I didn't parameterize the problem and it still came out correct. So, by ...
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1answer
58 views

Can someone explain the solution (provided) of this conical pendulum work problem [closed]

In the image, it looks like the tangential direction is always 45 degrees away from the string, not 90 degrees. Is it not the circular path that the solution is talking about?
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4answers
4k views

What is the electric potential at a point?

1) What does the electric potential at a point exactly mean? My teacher tells me that current flows from higher potential to lower potential but when I ask him the reason, he fails to give me a ...
2
votes
2answers
81 views

Work done by isothermal expansion from two different viewpoints

Consider an adiabatic system as follows. It consists of a gas in a container and a piston. Initially, the system is at equilibrium and the gas inside it occupies a volume $V_i$ at a pressure $p_i$ ...
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0answers
41 views

Can Somebody give me Questions [closed]

Can someone give me questions on physics because I have my Examination tomorrow Class 9th (CBSE) topic : - Fluids(Density,buoyant Force , Archemedis Principal) , Work Power Energy(Work Basics, ...
17
votes
4answers
3k views

How can we move an object with zero velocity?

Consider there is a box of mass $m$ at rest on the floor. Most books give an example that we need to do a work of $mgh$ to lift the box $h$ upward. If we analyze this work done, the external force ...
0
votes
1answer
49 views

Hydrostatics , work Power and Energy [closed]

If a servant lifts 10 cubic meter of liquid from a tank, which is at a depth of 40m . If the work done by him is 1600J, then find the density of the liquid (g = 10 m/s^2)
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2answers
114 views

what is “work”? (of a force)

I would like to know why two forces (of different magnitudes but same direction) that we'd use sequentially on an object to move it by the same amount twice, will produce two different values for the ...
-1
votes
1answer
65 views

Work Power & Energy Question [closed]

If a person starts from rest with an acceleration of 10 m/s^2 and applies force of 1000N then What will be its work done at the end of 20s . If the object moves in the horizontal surface? Can ...
0
votes
2answers
259 views

Rolling disk in inclined plane and flat plane? [duplicate]

A disk is rolling (not sliding) in the inclined plane with initial velocity of zero. So there is friction between disk and plane. But when we use the energy conservation rule, we consider as: ...
0
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1answer
42 views

To write work capacity of heart by symbols?

I know that the work capacity of the heart is Work capacity of the heart = pumping capacity x aortic impedance. I would mark work by W and impedance by Z. ...
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1answer
137 views

Measuring energy when no work is done — comparing push-ups to planks

tl;dr Is there any meaningful (physical) way to compare the energy expended in the exercise of doing $x$ pushups in $t_1$ seconds, vs the exercise of doing the plank for $t_2$ seconds? I'm ...
0
votes
2answers
261 views

In Which of the following situations would force be exerted on on object and no work be done on the object?

Consider the following question: In which of the following situations would a force be exerted on an object and no work be done on the object? I. a centripetal force is exerted on a moving ...
6
votes
2answers
119 views

While holding an object, no work done but costs energy (in response to a similar question)

I read the answer to Why does holding something up cost energy while no work is being done? and wanting to know more, I asked my teacher about it without telling him what I read here. Instead of ...
1
vote
1answer
351 views

Why doesn't the potential energy of any object equal 0

Consider a particle on the ground. This particle is raised by a force of magnitude $mg$ to a height $h$ above the ground. At this point, the work done on the particle by the force is $mgh$, which is ...
4
votes
4answers
321 views

Sign of Work and potential energy in electrostatics

Conceptual question: Suppose we have a configuration of point charges. If the potential of the energy of the system is negative, this means work is positive. I'm kind of rusty with my mechanics, ...
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0answers
39 views

Work done on an object from different frames

Consider this situation: A car is moving on a road and applies brakes. The road exerts a force $F$ on the car, due to which the car stops in $S$ meters. Clearly, the work done by the road on the car ...
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1answer
52 views

Why is the potential energy of a particle $mgh$ regardless of force?

Consider a particle raised to height $h$ by applying a constant force of $F$ vertically opposite to the direction of force of gravity on it. The potential energy of the particle is $$W = mgh$$ But, ...
1
vote
1answer
1k views

Calculate work done in an inclined plane [closed]

How can you calculate the work done by a force (of unknown quantity) exerted on a 10kg block on an inclined plane. The force is pointing upwards and parallel to the incline (which is inclined 30 ...
0
votes
2answers
64 views

How come weight doesn't affect the rebound height on a net?

According to my text book two unequal masses, (80kg and 50kg) fall on a net and the work done by that net is calculated by $\frac{1}{2}kx^2$. This work is then transformed into kinetic energy for both ...
0
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1answer
151 views

How to calculate work when a block is moving with constant velocity?

How to calculate work when a block is moving with constant velocity? As we know $f=ma$, and for constant velocity $a=0$, so $f=0$ and $w=fs=0$? Can anybody make it clear?
0
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1answer
156 views

Is it true that a Space Shuttle launch is powerful like an “average” nuclear explosion?

Kind of an odd question here. First let's define what an "average" nuclear explosion is, because that's quite a controversial term - "average". Considering that the peak of nuclear tests was at the ...
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3answers
1k views

A chain 64 meters long whose mass is 20 kilograms is hanging [closed]

A chain 64 meters long whose mass is 20 kilograms is hanging over the edge of a tall building and does not touch the ground. How much work is required to lift the top 3 meters of the chain to the top ...
1
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1answer
132 views

Work done by an expanding gas

Today in an engineering thermodynamics lecture, the professor gave an example of a gas doing work. We had a cylinder full of helium at a pressure of something like 200 kPa absolute and the valve was ...