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

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10 views

How is power of a water pump related to amount of water delivered from pipe?

My book says: Suppose a pump motor is used to deliver water at a certain rate from a given pipe. To get n times the water from same pipe in same time the power must be increased by $n^3$ ...
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3answers
40 views

How is Work by a System Interpretated in the First Law?

Good evening. I've happened to be sitting down today and just couldn't wrap my head around this question which seems rather simple at first. From reading about the first law and sign conventions as it ...
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1answer
44 views

How can we account for a friction force changing sign in a conservation of energy equation?

I want to solve a simple mechanical problem whereby three forces act upon an object. $F_1 = (10 - x)$ N $F_2 = -3 N$ (friction force) $F_3 = -10x$ N So at $x$ = 0 we see that $F_1$ + $F_2$ + $F_3$ ...
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2answers
87 views

How does pressurized gas constantly push?

If a gas, such as hydrogen, is pressurized into an air tight container, a force in terms of pascals (or whatever unit you want to use) is exerted, correct? That is what pushes against every surface ...
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1answer
30 views

Virtual work (generalized forces) for rotation with Euler angles

Here is what we know from virtual work: \begin{equation} \delta W=\sum_{i=1}^N{\vec F_i\cdot\delta\vec r_{i}} \end{equation} Where $N$ is the number of bodies in the system. I am considering a ...
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45 views

When is work done on or by something?

An example, here what my textbook says: When charges are released In electric fields charges experience the force causing them to accelerate along electric field vectors. Positive charges ...
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2answers
1k views

Having trouble understanding the work energy principle intuitively

I'm having trouble understanding the work energy principle intuitively. This is what I'm solid on so far: If you have a ball rolling down a hill, it loses potential energy and gains kinetic energy. ...
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136 views

Work and Free Body Diagrams

I am a bit confused with how to find work when there is a free body diagram. I am trying to work out this problem, and in it a box is being pulled at a constant speed by a rope at a constant angle ...
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4answers
145 views

What exactly is work?

What exactly is work? My book confuses me: a force can lift an object to a height h, or it can accelerate an object through gravity. In all these cases, a force displaces an object and change the ...
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2answers
247 views

Why does the coefficient of performance need to be calculated with $W + Q$?

How much work must a heat pump with a COP of 2.50 do in order to extract 1.00 MJ of thermal energy from the outdoors (the cold reservoir)? The first formula that came into my mind after reading ...
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31 views

What is the work done?

A painter uses 1.93kJ of mechanical energy to pull on the rope and lift a 20kg paint barrel at constant speed to a height of 7.5m above the ground. How much work was done lifting the paint barrel? ...
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3answers
41 views

Is work-kinetic energy theorem useless?

This is how my book explains it: $W_{net} = \delta K$ Since the net work is tied to changes in kinetic energy and changes in speed, a mass must accelerate in order for net work to be nonzero. ...
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1answer
49 views

Work done by friction on a ball flying through air [closed]

A baseball of mass 145 g leaves a pitcher’s hand at 150km/hr, but due to constant air resistance, it arrives at home plate 20.0m away traveling at 145km/hr Assume that the magnitude of the ball’s ...
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4answers
4k views

Proof of conservation of energy?

How is it proved to be always true? It's a fundamental principle in Physics, that is based on all of our currents observations of multiple systems in the universe, is it always true to all systems? ...
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2answers
84 views

How this formula for work follows from the definition?

If a particle moves along a path $\gamma : I\subset \mathbb{R}\to \mathbb{R}^3$ then the work done by a force $\mathbf{F}$ is defined by $$W = \int_{\gamma} \mathbf{F} = ...
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1answer
37 views

Net work done by projectiles?

When the projectile is in motion what is the net work done on projectiles? What i think? 0 first view: We know when we throw projectiles the initial KE and final KE is 0. So from work energy ...
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4answers
392 views

A confusion regarding an example in The Feynman Lectures

In The Feynman Lectures, In the chapter entitled Work and potential energy, Feynman states: The work done in going around any path in a gravitational field is zero. This is a very remarkable ...
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3answers
69 views

How does The work done in going around any path in a gravitational field is zero implies conservation of energy?

In The Feynman Lectures, Feynman states: The work done in going around any path in a gravitational field is zero. This is a very remarkable result. It tells us something we did not previously ...
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1answer
22 views

Can the energy/power required to mix two fluids together be calculated?

Given two fluids; say for example oxygen and nitrogen gases. By simply introducing, again for example 1 liter of each gas into a closed container, the process of diffusion alone will eventually cause ...
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1answer
36 views

Isn't the data insufficient in this problem?

take a look at this problem: a 1000 kg roller coaster car is towed at a constant speed up a 40 meters hill, what is the work done by the tow rope? don't we need the slope of the hill and the static ...
2
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2answers
131 views

Factors on which Coefficient of restitution depend

What are the factors on which coefficient of restitution depend? What is the reason for more coefficient of restitution of two glass balls (0.95) than for two lead balls (0.20)?
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1answer
58 views

Work done by battery and potential energy of a capacitor

I have a doubt about the work done by a battery and the potential energy of a capacitor? 1- Consider a circuit where the capacitors are connected to the terminals of a battery. Through calculations ...
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1answer
46 views

Friction as a Non-conservative force

Intuitively, one can find friction to be a non-conservative force. How can one prove that it is non-conservative?
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28 views

Question about pistons and how their volume is affected by particles?

I can't find an answer to this anywhere. When pressure is maintained in a piston and an ideal gas is injected into it (again, with no change in pressure as it is injected) the piston is displaced ...
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2answers
1k views

Work done against gravity [closed]

The work done against gravity is $mgh$, well at least that's what my textbook says. I have a question: I can apply a force say 50N, so total work done = $mgh + mah$. Where $ma$ = Force. But the truth ...
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63 views

Why is the net work done in a pulley-string system zero?

In any pulley system, where the pulleys and strings are massless and frictionless, why is the net work done by Tension zero?
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2answers
109 views

How can magnetic fields have energy and yet be unable to do work with that energy? [duplicate]

Magnetic fields can't do work. However, we use the following equation to describe the energy density of a magnetic field. $u = \frac{B^2}{2\mu_0}$ The term energy density suggests that the magnetic ...
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4answers
925 views

Does stopping the same bike and rider at the same velocity with the front brake require less energy than the back brake?

It's the same body made by the rider and the bike moving at the same speed. So, even though braking on the front/back alters the normal forces on the opposite wheels thus creating more friction with ...
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6answers
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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 ...
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1answer
26 views

Distinguishing Isentropic Process; Are all things in an insulated cylinder considered reversible adiabatic?

How much work is necessary to compress air in an insulated cylinder from 0.20m^3 to 0.01m^3. Use T1 = 20C and P1 = 100 kPa. I don't need to solution or the answer. I already have it. But I think ...
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1answer
147 views

Potential Energy of Springs and Gravity, and Work of a force

I am currently really stuck on this problem and I am not sure how to actually solve it, I think I can reason it out logically but I do not know how to show it. Here it is and under I will show what I ...
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1answer
34 views

Work done by friction on a body?

I know that when a body slides over a surface, the work done by friction is not stored as potential energy in the body. It is dissipated in the form of heat. But why is it not stored as potential ...
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1answer
62 views

Help understanding work

I have this problem: An object with 800kg mass is lifted up 2.4m by a force $F$. How much work does the Force do on the object (gravity is the only other force acting on the object)? From what ...
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3answers
92 views

Derivative of kinetic energy [closed]

I read that the derivative of kinetic energy=$F\cdot v$. I tried to differentiate (1/2) mv^2 with respect to time but each time I am getting $m*v$ and not $m*a*v$ which solves to $F*v$. My efforts are ...
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3answers
54 views

Work in the First Law of Thermodynamics

The First Law can be stated as $\Delta U=Q-W$, where $W$ is the work done by the system. My question is what kind of work $W$ includes. $W$ certainly includes $PV$ work, i.e. expansion and compression ...
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1answer
44 views

Classical Mechanics — Sign of work done

It seems that work has two possible ways to decide it's sign: Whether you take the perspective of the system or the surrounding (whether you consider work done on the system as positive, or work done ...
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1answer
52 views

Trajectories piecewise smooth?

In my studies of calculus and real analysis I have found the proofs of several theorems, commonly used in physics, such as those concerning the conservativity of fields, for example like If ...
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2answers
41 views

Question on units for integrating F vs x graph

I had a homework problem with this graph of F(Newtons) vs x(meters). The graph has a straight line (constant slope) from (0,0) to (8,10). And the slope ((10-0)/(8-0)) came out to be 1.25, making the ...
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0answers
14 views

Reaction enthalpy-work relationship in a closed piston-cylinder assembly undergoing a chemical reaction

In an closed and insulated piston-cylinder assembly under constant pressure. From first law I should expect $-p(V_f-V_i) = U_f – U_i$ and thus $H_f = H_i$ and $h_f = h_i$. If an exothermic reaction ...
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1answer
32 views

How much energy is saved when using luggage with wheels? [closed]

How much energy is saved when using luggage with wheels as opposed to carrying the luggage? Thanks.
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1answer
40 views

Exercise about equilibrium and virtual work [closed]

Two railway carriages of mass $M_1=2m$ and $M_2=m$ are on a 45° inclined plane. A spring, parallel to the plane, keeps both carriages in balance against the gravitational accceleration. The ...
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2answers
47 views

Energy loss without work or heat?

Suppose we have a mass-spring system in equilibrium as in the above part of the picture(it's a frictionless surface). Then I attached a weightless rope to the mass from one end and a car from the ...
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2answers
30 views

Is net work and total work same?

According to my text book Total Work = Delta Kinetic Energy = KEf - KEi But then work is defined to be dot product of Force (vector) and Displacement (vector). Also to my knowledge work is ...
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4answers
326 views

How can tangential acceleration from a radial force be explained?

A mass is attached to a rope, and put into a circular motion. If I pull the string from the center, the tangential speed of the mass will increase (by conservation of angular momentum). I am ...
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0answers
41 views

How to locate the initial speed? [closed]

I have this question: Two men were delivering a crate of mass $100~\text{kg}$ to a house up a hill which is inclined at $35^\circ$, when it dropped and slid down the hill. The coefficient of ...
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2answers
43 views

In what form is the energy stored in this situation?

Consider a hypothetical situation, A person is pushing a block of some arbitrary mass in vacuum (no external forces are involved) and due to this, if I am not mistaken, the person is doing work and ...
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2answers
85 views

What constitutes work?

I'm asked: "An object is moving along a floor at constant velocity. Thinking about this situation as realistically as possible, is work being done on the object?" And the solution is: "Work is ...
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1answer
50 views

What exactly is conservative vector field?

I'm studying calculus, but since the example involved a physical concept. I will ask here: This is how it goes: This means that in a conservative force field, the amount of work required to ...
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2answers
674 views

Does energy expenditure require movement? [duplicate]

In every formula I've seen that involves energy, I've also seen a distance element. Is there nothing that doesn't involve movement? For instance if I hold my arm out parallel to the ground with a ...
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0answers
49 views

What is the difference physiologically between running uphill vs. downhill? [closed]

In pure potential energy terms a person needs positive energy (work) to lift their body to a higher gravitational potential. When they turn around and run back down, the same transaction is reversed ...