Questions tagged [work]

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

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Part of physics answer I didn't understand, and don't have reputation to ask them. $10\,\text{ms}^{−2}$

When you lift your $2.5 \,\text{kg}$ laptop (a 15-inch Apple MacBook Pro, for example) by a foot, you do work of approximately $2.5 \,\text{kg} \times 10 \,\text{ms}^{−2} \times 0.3 \,\text{m} = 7.5 \,...
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How to check and find potential functions given a force?

I was given a force, let's say $F = 15xy$ N to the right which moves a system from $A(0,0)$ to $B(3,4)$ and was to find the work done by the force, in Joules. My approach was by using $\vec{F} = -\vec{...
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Neutral points in an electrical circuit?

I have been told that potential in an electric circuit is defined as the work done in bringing a unit test positive charge to that point inside the circuit. Thus it satisfies the premise that ...
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Multiple spring-block system. Question about method of solving [closed]

I dont know if these kind of questions are allowed so, sorry if i shouldnt be asking homework questions... This is how I attempted the question. Let the tension in the right upper string be T. Then ...
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Moving boundary work

Moving boundary work can be equated from $\Delta W = p dV$. So can we say that W is a function of V and p is the first derivative of W, f'(v)?
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Work-energy principle: What if there is no change in KE, but change in PE?

So I've been taught that the work-energy principle says that the total work done on an object is always equal to the change in kinetic energy of an object. Now let's say that I have a car moving up an ...
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Does fuel consumption depend completely on work done?

I recently encountered a question in a physics workbook, a car of mass m kg is lifted by two cranes to a height of h metres, the cranes lift the car in t1 and t2 seconds respectively (t1<t2), then ...
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How do you derive the equation that the total energy is equal to the sum of potential plus the kinetic energy?

In this stack-post, an equation relating the external work done and the change in potential and kinetic energy of the system was derived by the user Biophysicist. Given: $$ W_{ext} = \Delta K + \...
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Minimum velocity for a pendulum to rotate a quadrant [closed]

Suppose a pendulum is allowed to rotate in a vertical plane(z-x) shown below: What is the minimum velocity that it must start with such that it rotates an angle of $ \frac{\pi}{2}$ degrees? In the ...
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Why is work done not equal to force times time?

I am having an issue with the definition of work. I know there are several questions already posted which seem the same as this one but the issue is that all of them either haven't been answered or ...
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Does the Magnetic Field do work in Quantum Mechanics?

Let's say I have an electron in an infinite potential well. The Hamiltonian is given by: $$ \hat H | E_n \rangle= \frac{\hat p^2}{2m}| E_n \rangle $$ with $p$ being the momentum and $m$ being the mass....
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Finding the angle of inclination given the work done by friction [closed]

My question pertains to part (ii) of the following question: In part i, I found that the speed at point B is $ 7 m/s$. Now, in part ii, there are two ways to approach the question. The first uses the ...
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How can you conclude that gravity is a conservative force?

A force field $F_i(x)$ is conservative if for every curve $C$ from a point $y_1$ to a point $y_2$, we have $\int\limits_C F_i(x)\mathrm{d}x^i$, so that the energy difference between $y_1$ and $y_2$ is ...
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Expressing starting position of a roller coaster on a track so that it can then go through a loop de loop by unknowns [closed]

I would like to have the steps to do part (a) only. I tried using [P.E. at h1]=[(K.E.+P.E.) at h2] to find the expression but the mass m will be removed in the end, not fulfilling the requirement of ...
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Equation for the work done to bring in an small amount of free charge in a dielectric

Griffiths says: Suppose the dielectric material is fixed in position, and we bring in the free charge, a bit at a time. As $\rho_{f}$ increased by an amount $\triangle \rho_{f}$, the polarization ...
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How to derive that $\delta w = - PdV$?

I am not understanding how to derive this particular expression, which relates the inexact differential of work to the exact differential of volume, $$\delta w = -PdV $$ My attempt: Reversible work ...
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1answer
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Work done and point of application

I read some books and some articles regarding point of application but I could not understand what it really means Let's suppose you have a ball and you throw it on a rigid wall now the ball comes ...
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Minimum force to stand on flat ground and climb stairs? [closed]

What is the minimum force that we need to lift our body to walk up a flight of stairs? Let's say I weigh 50 kg and I walk up a flight of stairs. What the minimum force I need to apply to stand ...
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Can anyone help me in these question:(related to Work Done) [closed]

Can work done by Kinetic Friction on an object be positive? Zero? Can Static Friction do Non-zero work on an object? Can Normal Force do Non-zero work on an object?
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Is work done by a person while walking negative? [duplicate]

When a person walks (assuming the feet don't slip), the ground is pushed backward by the foot while the force of static friction opposes the force and the foot remains stationary while the upper body ...
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46 views

Does work between 2 bodies depend on their relative speed?

Imagine a car standing on the road. Now the car starts to accelerate. On the first part, the car accelerates from 0 m/s to 10 m/s. Some of the fuel was used during this first part. let's call that ...
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1answer
168 views

Doesn't $dP×dV$ contribute to internal energy change?

When the heat supplied to system is zero and change in internal energy is brought by work, it is said that $W=P(ext)×dV$ is the work done. Isn't that work done (causing internal energy change) due to ...
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In this problem, why is the work done by the spring not equal to the line integral of the spring force over its displacement?

Problem statement: In the given figure, two blocks A and B, each having a mass of 320 grams are connected by a light string passing over a smooth light pulley. The horizontal surface on which block A ...
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Can we define Kinetic Energy from non-inertial frame?

I have read somewhere that Work Energy Theorem can be applied even from non-inertial frame by adding work done by pseudo force. I further think that we need to take Kinetic Energy with reference to ...
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Work done by massless spring

Since net force on a massless spring is zero, work done on a spring should be zero, according to elementary work done $F \cdot dr$ since $F= 0$. Then why do we calculate it to be $\frac {kx²}{2}$? ...
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Better derivation for the gravitational potential energy

I was shown this derivation for the gravitational potential energy, and I'm not very happy about it assuming that $\frac{1}{\infty} = 0$. Is there a better derivation, either using a completely ...
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Work done in assembling a point charge is infinite [closed]

Griffiths says The energy of a point charge is infinite $$W=\frac{\epsilon_{0}}{2\left(4 \pi \epsilon_{0}\right)^{2}} \int_0^\infty\left(\frac{q^{2}}{r^{4}}\right)\left(r^{2} \sin \theta\; \mathrm{d}...
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How is it possible for the same force to do different amounts of work in two different inertial frames?

Consider an object which has been given a speed $v$ on a rough horizontal surface. As time passes, the object covers a distance $l$ until it stops because of friction. Now, Initial kinetic energy = $\...
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How is change in enthalpy in a cyclic process zero when work done is not equal to zero and the change in internal energy is equal to zero

We know that change in internal energy is equal to heat supplied - work done in a cyclic process. The change in internal energy is zero and work done is non-zero. This implies that the heat given is ...
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How to make sense out of Potential Energy?

My teacher says that Energy is in the form of Electric field. I've also seen the mathematical prove. (The amount of work done in bringing a charge from infinity to that point in the Electric Field) ...
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Work $U$ required to assemble a charge distribution

I'm reading Purcell's Electricity and Magnetism (p. 72) and it gives an relation between the work $U$ required to assemble a charge distribution $ \rho (x,y,z) $ and potential $\phi (x,y,z) $ of that ...
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Question on “The more information you have about a system, the more work you can extract from it”

This was said in the comments (#15/#27) of this Scott Aaronson post about "information is physical" and reaffirmed by Sean Carroll and praised by Scott among others. https://www....
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Potential energy to gain elevation

I did a calculation to see how high the energy in a cell phone battery could lift an adult assuming perfect efficiency but something seems way off. ...
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Work-Energy Theorem vs Angular Momentum Conservation in Central-Force Problem

I'm working on a problem from YK Lim's "Problems and Solutions on Mechanics". It is Problem 1016. Here is the statement of the problem: A mass $m$ moves in a circle on a smooth horizontal ...
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Sign of shaft work done when piston moves upward

If the piston shown above moves upwards a distance 1 m the shaft work (according to the textbook solution to a related problem) is 1334 J. Shouldn't the sign of work be negative because the shaft ...
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Vertical circular motion inside a tube and with a light rod [closed]

I have a doubt that when the initial velocity given to a mass connected to a light rod fixed at one point, is $\sqrt{4gr}$ (given at the lowest point) then does it complete a circle or just reach ...
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How does energy remain constant when the NET work done is zero?

If I were to go from X to Y and then back to X, the NET work done by me would be zero. But, how will the energy remain constant? Really confused about energy and work here. Energy is the ability to do ...
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Work is a path function: it cannot be expressed as a difference between the value of some property of the system in two states

Why do we not define work done as the difference between two quantities that depend entirely on the initial and final states. Why is work a path function? What is the reason?
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Gravitational potential energy of an $n$-body

In my CIE A level course, the gravitational potential energy of a mass in a gravitational field is defined as the work done in bringing the mass from infinity to that point without changing it’s k.e. ...
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Proving equivalence between Mechanical work and Heat

At 12:20 of this video lecture, while proving temperature and heat relation using a paddle wheel and hanging a mass to it, professor Bob Field writes down the change in temperature as $\Delta T = \...
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How is centrifugal force doing work here?

Q) A plane spiral made of stiff smooth wire is rotated with a constant angular velocity $\omega$ in a horizontal plane about the fixed vertical axis O. A small sleeve M slides along that spiral ...
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How does work done to move an object scale with more/less gravity?

First let me say that Physics is not my area of expertise and my knowledge from school is pretty rusty, so I apologize in advance if I am asking a totally stupid thing or I have a mismatched ...
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Trouble in understanding question related to the work, energy and power chapter about pendulum

Two pendulums of masses $m_1$ and $m_2$ ($m_1>m_2$) and strings of same length are taken. The densities of the both the bobs are the same ($d_1=d_2$), if we compare the time period of the two ...
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Is the work done by a spring and the work done on a spring the same?

Lets imagine we have a spring of a linear characteristic such that the force the spring exerts is proportional to its deformation $\delta$. The spring is attached horizontally to a wall, now if we ...
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How can we choose any level for gravitational potential energy to be zero?

In my book, I read that we can choose any level as Zero Gravitational P.E. and measure height of objects above it and call its energy 'mgh'. But by saying that all the points on that level is of zero ...
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If both forces are equal and they are opposite in direction how can an object be displaced?

In order to calculate work done against force of gravity we consider we have to apply a force of $F=mg$ on a object and we have to do work $W=mgh$. If gravitational force is also $mg$ how can an ...
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Work done in an Adiabatic process

I was reading this chapter, and am confused with the concept provided under heading WORK (on page 162). The term "adiabatic" as I understand it, involves,absolutely no exchange of energy ...
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Inconsistency in applying work-energy theorem in the classical problem of a kink on an inclined wedge

Consider the typical problems of mechanics where we had to find the velocity for some mass which reaches bottom of a wedge after metting some changes in the wedge angles (kinks). The following is a ...
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Determining barbell weight capacity

Is there any way I can at least approximate the maximum weight capacity of a barbell based on things like the length and weight of the barbell? If anyone has an article I can read into for that, that ...
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Interpreting the Negative Sign in Simple Harmonic Motion

What I Know: $$ \vec F = -k \vec x $$ where the negative sign indicates the Force acts in the opposite direction to the displacement. If we were to take the integral so... $$\int_{x_i}^{x_f} Fdx = -\...

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