Work and energy Definition and 332 Threads

How can we explain the effectiveness of a force in terms of energy and work? For example, a boxer's punch has a similar amount of kinetic energy to a 9x21mm bullet, yet the bullet has far greater penetrating power. From what I understand, this is due to the bullet’s force being applied over a...

This may seem like an obvious and foolish question intuitively, but I am curious about something. Let's assume we are performing a biceps curl exercise. To properly analyze human movement, a much more complex process is needed, but I will simplify it as much as possible. As the name of the...

The work done by A on B as Wab, and the work done by B on A as Wba. I have always thought that Wab = -Wba generally always holds true. Looking at it from the perspective of energy transfer: "A do 10J of work on B." "A transfer 10J of energy to B." "B received 10J of energy from A." "B do...

I asked a similar question yesterday, but I have additional queries, so I'm posting another question. If I pull an object connected to a string with a force of 10N in a straight line for 1 meter, I would have done 10J of work on the object. According to the law of conservation of energy, I would...

When we are acting with some force ##F = mg## on an object of mass ##m## vertically in the positive ##y## direction, we are doing work that is equal to the work done by gravity on the same object, but of course opposite in sign. It means that net work is equal to zero, hence no change in kinetic...

Electrostatic potential $$ \Phi(\vec{r})=k \int \mathrm{d}^{3} r \frac{\rho\left(\vec{r}^{\prime}\right)}{\left|\vec{r}-\vec{r}^{\prime}\right|} (i) $$ with $$ k=\frac{1}{4\pi\epsilon_{0}} $$ in SI units. What work is required to move a point charge q from infinity to the center of the through...

What is the work done by gravity in moving the particle from a distance of ##\infty## to a distance ##R## from the centre of the Earth (where ##R## > the radius of the Earth)? The answer is obvious, since the displacement and the force of gravity are in the same direction. Therefore, gravity...

Guys, please look at the following question I am aware of how to take a dot product of 2 vectors whose i,j,k components are given. My issue is with both integrals. I feel it should be '-dx ' rather than dx because x is decreasing , same as in '-dy'.and I'm taught that if x is decreasing then...

The question is easy. I merely have a query: When the bow string is released, the potential energy stored in it ##U = \frac {kx^2} {2}## is all transformed to kinetic energy ##K = \frac {mv^2} {2}##, so we have:$$v = \sqrt {\frac {k} {m}}x$$ I now need to eliminate ##k##, so I can use ##k =...

I'd have no problem with this sort of problem if the force were a function of position. But here, I'm not sure where to go. Perhaps I'd start with an expression for the work done over an arbitrary distance if the force is given by ##g(v)##:$$W = \int_a^b g(v) \, dx$$ Not sure what to do next...

If you use work energy, you can get 0.5*k*x^2 = 0.5*m*v^2 to get the velocity if you pulled the spring a distance x. How come you cannot do kx*(delta t) = m*v to get the initial velocity and what would be the delta t value?

I think that the work is meant to be work done for instance in power stations. Or is it similar to work I do on a body when I lift it for example? But how can we then do that work on our Earth? I just need to understand the task, otherwise I want to solve it myself. The problem involves...

Knowing that negative work occurs when the force applied to an object opposes the direction of displacement, and that the direction of acceleration vector should align with the force vector, I assumed the correct answer was that the indication of negative work comes from negative acceleration...

My solution is different from the official solution and I don't understand what I did wrong. Here is my solution: The magnitude of the initial velocity is ##|v_0| = 12.0~\rm{m/s}##, so the vertical component of the initial velocity is ##v_{0-y} = (12.0 \sin{25^{\circ}})~\rm{m/s}##. Then I use...

Power P = F x v,where F is force and v is velocity, if power remains constant then i think force can not remain constant as it will change the velocity v, but the solution I found is, F = ma, v = at, so, P = F x v = ma x at = ma2 t, after that calculus comes to show that displacement is...

The answer is .32m. I set the elastic potential energy as equal to the work, but at first I put the force in the work equation as (F elastic - F kinetic friction) times distance and rearranged. 1/2kx^2 = (kx-Ff) d (0.5) (22) (0.035)^2 = (22 x 0.035-0.042) d 0.013475= 0.728 d 0.013475/0.728 = d...

What force causes the surface to move to the left? Can I say that it's due to the force component of the weight along the vertical force of the surface?

Hello, Suppose I have a spherical hole in a elastic infinite space. I apply a time-dependent pressure to the inner surface of the spherical hole. I know p = f(t). If I only consider this as an elastic problem, no failure happened, how can I calculate the work done by p during the time from 0...

Hi, everyone! There are a lot of work energy conservation laws and I get confused which one of them summarizes all of them. Which one I should keep with me and rest should be easy to derive on spot ? 1. ##\Delta E_{mec}=0## 2. ##\Delta E_{mec}=W_{ext}## 3.##\Delta E_{mec} + \Delta...

Hi, Everyone! This is the page(first image) from Principle of physics by resnik. I want to ask the definition of work(##W=F(x) \Delta x##) by variable force here is somewhat different from the usual integral version. I don't understand how is this valid definition? Secondly, how did they reach...

a) ##\rho = \frac{I}{c} = \frac{F}{A}## for a perfect absorber ##F = ma## where ##a = \frac{c}{t}## ##\frac{I}{c} = \frac{mc}{tA}## ##I = \frac{I^2 tA}{mc^2} = \frac{P}{A}## ##P = \frac{I^2 tA^2}{mc^2} = \frac{W}{t}## ##W = \frac{I^2 t^2A^2}{mc^2}## I am unsure what A is. I think it should be...

Here's my list of variables and things to account for: m=100kg Wnc=5000J Wfriction=-500J -Kinetic energy will be doubled (though I don't know how that plays into it exactly) -I don't think there's any PE because it's on level ground My idea of what the equation might be: Wnc +1/2mv^2initial =...

What is the need to introduce the concept of work and energy when the motion can be completely understood by the concept of force and acceleration and momentum and velocity and displacement, etc? Why do we need to understand the same thing once again in terms of Work and energy? Also the kinetic...

1. From resnik, Halliday “Kinetic energy K is energy associated with the state of motion of an object. The faster the object moves , the greater is the kinetic energy” If I am right this means that greater the kinetic energy, greater is its speed. 2. Force transfers energy to the body due to...

Hello, I’ll start by saying I have the answers and the steps to the solutions, but there’s a comprehension disconnect somewhere that I’m trying to figure out. There are two parts to my question but the second one may not apply depending on the answer to the first. I wasn’t sure from the forum...

I spend a lot of time thinking about collision problems because for me they are both extremely interesting and often very difficult to grasp when one thinks about them beyond the basics we are taught in introductory or even intermediate university courses. Suppose there is a perfectly elastic...

u = (9*10^9)(1.61*10^-19)^2 * (1/[3*10^-15 ]- 1/[2*10^-10]) u = 7.68*10^-14 J but here the question. I have been taught that W= -U so shouldn't the answer be negative?? When i look up at the solution all other sources say that the W = U and therefore the answer is in postive.

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Suppose I am sliding a block very slowly on a rough surface. If the block has traveled ##d## distance then work done by me is ##W_1=\mu mg d## and that by friction is ##W_2=-\mu mg d##. Now the energy transferred from me to block is ##\mu mgd## and that taken by friction from block is ##\mu mgd...

This is the solution from my textbook, and I have some questions about the method The mass of hanging chain : $$m_h =\frac m 5$$ the center of mass of the hanging chain : $$h_1 = - \frac{1} {2} \cdot \frac L 5 = - \frac L {10}$$ (the minus sign here means that it is under the table surface)...

Guys, I have a problem that really needs you guys to help, I know it is a stupid question but please bear with me: Context: You have a block on a slope(has friction) you use a string to pull the block up with constant speed. Problem: So according to the network theorem, the work net is equal...

As stated, part (a) says that the work done by the gravitational force ##\vec{F_g}## is 59 kJ. If ##W_T## is the work done by the elevator cable during the 12 m fall, then using the work-kinetic energy theorem, \begin{align*} K_f -K_i &= W_g + W_T\\ \frac12m({v_f}^2 - {v_i}^2) &= 59000 + W_T\\...

i can't manage to grasp the concept of PV work in thermodynamics, for example we all know that W= integral(F*dx) like here but this says that, at the end, W doesn't really depend on the gas temperature or reversible process crap at the end W is simply a constant, atmospheric pressure is...

This looks like a classical setup but I can't find a solution. We can calculate the energy of the system by looking at the work done by the gravity and the spring. But how do we divide the energy between the kinetic energy of the pulley and the rotation of the pulley?

Hello I've written that homework statement as an example to illustrate my doubt: How can I tell if a force is conservative or not? I've read that, if the curl of the force is 0, it's conservative. But what about the friction force (##f=\mu N##)? Its curl is also zero, but it's not conservative...

Summary:: Would energy method give us a different answer from conservation of angular momentum? Hello, I do not know how to type equations here. So, I typed my question in Word and attached it here. Please see photos. Note: This question is not a homework. I did not find it in textbooks or...

Wikipedia says, Unlike a free expansion , in Joule Thomson expansion work is done causing the change in internal energy. Whether the internal energy increases or decreases is determined by whether work is done on or by the fluid; that is determined by the initial and final states of the...

This problem was from the chapter on Work and Energy so, I thought of using the principle of conservation of mechanical energy. Clearly, the potential energy of the block decreases by mgh (assuming the block has mass m). This energy should have been converted to kinetic energy, but it clearly...

Diagram attached at the endI personally think there's something wrong with this question, and I'd like if someone can tell me whether it's the question that is wrong or my approach. If I attempt the solution thinking that M should be stationary, the solution is simple. 0 - 1/2 mv^2 = -mgh...

A recent thread posed the question whether work is done by static friction in the case of an accelerating car. Before I had a chance to reply, the thread was closed on the grounds that the subject was "beaten to death". Undaunted, I am determined to deliver the coup de grâce here with a simple...

I used work energy theorem between initial top point and point x along the incline(downwards) i got the expression of v then diffrentiated it to get a maxima but it gives me a wrong ans which is 10/6 but the actual ans is 10/3 please tell me what i did wrong

The problem is based on a projectile-spring launcher. A ball is loaded into a tube that pushes back a spring and is then launched. The ball was launched straight horizontally not at an angle. I'm trying to find the work done on the ball by the spring. The info I have: Displacement of spring =...

I first wrote down that 55% = Eout/Ein I also know that W = (Facos20)(4) and I substitute it into the first equation 55% = Eout/[(Facos20)(4)] But I'm missing two variables here. Did i forget something or is the question missing some information?

When you say ##i = \frac{dq}{dt}## it makes sense since current is the flow of charge over time. But why was voltage defined as ##v = \frac{dw}{dq}## ? What made physicians define it in this way? Is there a mathematical way that can lead to this definition or did they define voltage just on the...

TA = Ec 0,7*m*g*d = (m*v² /2) 1,4*g*d = (400/12,96) 14*d = (400/12,96) d = 2,2 m No

Homework Statement: A perfect hemisphere of frictionless ice has radius R=7 meters. Sitting on the top of the ice, motionless, is a box of mass m=7 kg. The box starts to slide to the right, down the sloping surface of the ice. After it has moved by an angle 11 degrees from the top, how much...

Homework Statement: Hetsut is the foreman of a construction project in ancient Egypt. He needs to move a giant block of stone, of mass 12 metric tons, from the docks to the temple grounds. He can go along the roads by traveling 295 meters east, then 89 meters north. Along the roads, the...