# Work Definition and 330 Discussions

In physics, work is the energy transferred to or from an object via the application of force along a displacement. In its simplest form, it is often represented as the product of force and displacement. A force is said to do positive work if (when applied) it has a component in the direction of the displacement of the point of application. A force does negative work if it has a component opposite to the direction of the displacement at the point of application of the force.
For example, when a ball is held above the ground and then dropped, the work done by the gravitational force on the ball as it falls is equal to the weight of the ball (a force) multiplied by the distance to the ground (a displacement). When the force F is constant and the angle between the force and the displacement s is θ, then the work done is given by:

W
=
F
s
cos

θ

{\displaystyle W=Fs\cos {\theta }}
Work is a scalar quantity, so it has only magnitude and no direction. Work transfers energy from one place to another, or one form to another. The SI unit of work is the joule (J), the same unit as for energy.

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1. ### I Does dW/dx = Fx and dW/dy = Fy?

Since dW = F dot product dr dW/dr = F So dW/dx = Fx and dW/dx = Fy? I am looking at conservative forces where dU/dx = Fx and dU/dy = Fy
2. ### F dot product dr problem

y = 10*(1 + cos(0.1*x)) --> dy/dx = -sin(0.1x) dW = F*dx + F*dy = 10*sin(0.1*x)dx + 10*sin(0.1*x)*-sin(0.1x) integrating we have -100*cos(0.1*x) -10*sin(0.1x)^2 from 0 to 10*pi = W = 43 J. The answer says 257 J. Where am I wrong here?
3. ### Finding kinetic energy and initial velocity of a cart over time

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 =...
4. ### Work done on dipole and potential energy in uniform electric field

I encountered a problem regarding the appropriate sign needed to be taken for the work done on a dipole when it rotates in a uniform electric field and would appreciate some help. The torque on a dipole can be defined as τ=PEsinθ The work done on a dipole to move it from an angle ##\theta_0##...
5. ### Work to bring a charge to the center of two quarter circles

By measuring angle \theta from the positive ##x## axis counterclockwise as usual, I get ##d\vec{E}=k( (\lambda_2-\lambda_1)\cos(\theta)d\theta, (\lambda_2-\lambda_1)\sin(\theta)d\theta )## and by integrating from ##\theta=0## to ##\theta=\frac{\pi}{2}## I get...
6. ### I Bernoull's Equation Derivation From Work - Energy Principle

Work - Energy principle states that work of resultant force or sum of work of all forces acting on some system equals change in kinetic energy of the system. For inviscid fluid flowing in a pipe such theorem can be used to derive Bernoulli's equation because as fluid flows it is subjected to...
7. ### Number of moles necessary to get piston back to initial position

a) ##T_A=\frac{p_AV_A}{nR}=300.7K, P_A V_A=kL^2=nRT_A##, ##P_B S=k\frac{L}{2}\Rightarrow P_B V_B=k(\frac{L}{2})^2 \Rightarrow P_B=\frac{kL^2}{2V_A}=\frac{P_AV_A}{2V_A}=\frac{P_A}{2}##, ##W_{spring\to gas}=\int_{L}^{L/2}kxdx=-\frac{3}{8}kL^2=-\frac{3}{8}nRT_A####\Rightarrow Q=L+\Delta...
8. ### Question about equipotential lines and the work done moving along them

hi guys i have a conceptual question .As you know equipotential surfaces is one on which all point are the same potential there is no work required to move a charge from one point to the other . So my question is how can we change the locotion of a particle without using any force ?
9. ### 2 Carts on a Track Compressed by a Spring -- What are their Velocities?

a)What is the total energy in the system? Only energy acting on the system assuming the track is level and there is no potential energy of the carts, is the potential energy of the spring. Comes out to 7.8125 using the potential energy of a spring equation. b) What are their velocities if the...
10. ### Finding tension to find work [SOLVED]

Confused on how to find tension in rope (this would be the force acting on mass 2 that is causing work). Fnet wouldnt be 0 since the speed isn't constant and no acceleration is given. I'm sure I'm suppose to use the masses in an equation somehow, but I'm not sure how. It makes sense that the...
11. ### Work Done on an object by 3 Forces (Very Confused)

Here's a diagram of the object My Question: My friend and I were solving this problem. We both found Fxnet and Fynet. However to find work I did W= Fnet*d whereas he did W= Fxnet* d. He claims that since it's sliding on the floor it can only go in the x-direction, and it can't go in the...
12. ### Question about work and finding the force of friction

I drew a force diagram, Normal force up, weight down, force of friction to the left, and Force applied 20 degrees above the positive x axis. I need clarification to find the force of Friction for part B. Should I set Force of friction equal to mu · normal force or should I use newton's second...
13. ### Equipotentials and Conductors

Here I am going to include the proof provided by my book. It is quite a splendid explanation, though there are a few key points I have yet to fully understand. If the electric force by the electric field on the charge at the surface of the conductor is conservative (which it is), then why is...
14. N

### How many hours do employees actually work?

Most companies specify full-time jobs as working 8 hours per day, or 40 hours per week. Some of these jobs have strict time schedule like between 9-5, others have a more flexible time. My question is more about the jobs with flexible time, since these jobs allow you to stay in the office for as...
15. ### Is Gravity the only force doing work on a roller coaster cart?

Why I think gravity *is* the only force doing work on the rider: 1) The only forces acting on the rider are gravity and the normal force. Broken down into their component vectors, we have: -> The component of the force of gravity moving parallel to the rider's direction of motion -> The normal...
16. ### Power generated by an engine

I'm really struggling with this problem. I can't understand which are the forces that i need to calculate work. Probabily when the sand falls the force of which i need to calculate work is weight force, but which is the force that carries the sand at the top of the roller?
17. ### Work Done by an Induced Electric Field

I have drawn a picture of what the induced electric field will look like, and I have determined its magnitude both within and outside of the magnetic field. I was able to get the right answer for part (b) with this information, but I don't understand why the answer for part (c) is 0 J. It...

19. ### Gas - cylinder - piston problem

Summary:: Seeking explanation to classical gas - cylinder - piston problem, not the solution. Problem 1.15 from 7th edition of Introduction to Chemical Engineering Thermodynamics by Smith, Van nes and Abbot) Classical problem, given: - gas in a confined cylinder - piston with weight is placed...
20. ### What is the work done to move this Charge?

I found two formulas to calculate the work done. One is with this path integral: ## W_{AB}## = W(## r_A,r_B ##)=q* ## \int_{r_A}^{r_B} E*dr ## but here is the one I tried to use: ## W_{AB}## = q*Δ U = q*(## \frac {kQ} {r_A} ## - ## \frac {kQ} {r_B} ## ) Now heres my problem, what are...
21. ### What is the concept of work?

if I shoot the football, the ball will recive a force in specific direction, and it would follow that direction. Does the work is done by me when I shooted the ball, or the ball does work when it moves all the period after my shooting ? the work includes force and displacement , so who does the...
22. ### A Theoretical status of the Landauer Principle

I am interested to understand the current theoretical status of Landauer's Principle and related ideas. I am looking for key papers and results in the subject. I will highlight one key paper. An improved Landauer principle with finite-size corrections Abstract: Landauerʼs principle relates...
23. ### Question about net work and displacement

I know that by physics definition if displacement is zero, work is zero. However, if I push an object 5 m to the east, and then move to the other side of the object and push it 5 m back to the west. I think in this case I have always done positive work on the object and hence the total work...
24. ### Physics Jobs during a PhD

Hello all: I am asking for your personal experience , did you were able to work normally with your PhD studies ? What kind of work ? Is it easier with theoretical PhD or an experimental one ? Best H.B.
25. ### Energy and non-conservative forces

I feel like it would go on the side of the energy the object has where it starts - an object dropped off a cliff would be modeled U - W = K but an object thrown upwards from ground level would be K - W = U. I am not sure though.
26. ### How do adapters work? (SATA to USB, or VGA to HDMI)

Does adapters (exp: SATA to USB or VGA to hdmi) work with special softwares for conversion or are they only electronic circuits which gets and directs input signals to correct output pins?
27. ### Confused by the relationship of work and kinetic energy

So the equation for work is W = F * s F = m * a, so W = m * a * s Transferring this to units of measurement gives us: J = kg * m * s-2 * m Or simplified: J = kg * m2 * s-2 Transferring back to units of quantity: W = m * v2 How can that be correct? Obviously Ekin = 1/2 * m * v2. Where did that...
28. ### What is the direction of work in this figure?

iam not sure of the direction of work , is it positive becouse pulleys change the direction of the force ? or is it negative because of the arrow that indicates the direction of acceleration ??!
29. ### How to work out Joules needed to perform work

Hello all! First post here, and I apologize in advance if this question belongs elsewhere- I'll learn as I go. I am interested in knowing more about energy and performing work. In particular, if I have an object I would like to lift, how much energy I need to expend to do that. Take for...
30. ### Internal energy in ideal gas

I have the definition of change in internal energy. $$\Delta U = Q - W$$ I can get the work by $$W = \int_{V_1}^{V_2} p dV = p \Delta V$$ however the pressure isn't constant so this wont do. ## W ## is work done by the gas and ## Q ## is amount of heat energy brought into the system. I'm...
31. ### Calculate the impact force when falling from a height

To find vx vx = dx/t = 3.86 m/1.5 s= 2.573 m/s To find Ek Ek = ½mvx²= ½(79.4)(2.573)²= 262.8 J W = FnetΔd Fnet = 262.8 J/ 3.86 m = 68 N He hits him with a force of 68N
32. ### How far does the block slide? (work, spring, incline)

Homework Statement The system is released from rest with no slack in the cable and with the spring stretched 225 mm. Determine the distance s traveled by the 3.2-kg cart before it comes to rest (a) if m approaches zero and (b) if m = 2.5 kg. Assume no mechanical interference and no friction...
33. ### Job Skills Github for data science

Hi I have the educational background to do a few jobs I have seen posted as "data scientist" or "data engineer". However, I keep getting told that to get a job like that with my background, in mathematics, I need to post code examples on Github. However, I always feel like my ideas are either...
34. ### Emptying a well using a pump

Homework Statement A well has a diameter of 6 m and a height of 15 m.2/3 of volume of the well is filled with water.A pump can vacate 1/3 of volume of water from the well in 7 minutes 20 seconds.What is the power of the pump? Homework Equations W=mgh, P=W/t The Attempt at a Solution The...
35. ### Problem involving energy/motion

Homework Statement A ball of mass m=0.300 kg is connected by a strong massless rod of length L = 0.800 m to a pivot and held in place with the rod vertical. A wind exerts constant force F to the right on the ball as shown below. The ball is released from rest. The wind makes it swing up to...
36. ### DIY Stirling engine project

hello, I had made an DIY alpha type Stirling engine for my physics project and now I have to write an report about the relationship between the heat given to the engine and the motion of the wheel. I had searched a lot about Stirling engines and I learned about work, energy, efficiency...
37. ### How to calculate the work done

Homework Statement A sledge loaded with bricks has a total mass of 18.0 kg and is pulled at constant speed by a rope inclined at 20.0° above the horizontal. The sledge moves a distance of 20.0 m on a horizontal surface. The coefficient of kinetic friction between the sledge and surface is...
38. ### Calculating the work done using a line integral

Homework Statement a) A point charge + q is placed at the origin. By explicitly calculating the relevant line integral, determine how much external work must be done to bring another point charge + q from infinity to the point r2= aŷ ? Consider the difference between external work and work...
39. ### Calculating the final speed w/ work & friction

The problem is asking me to find the final speed of a 1100 kg car traveling at 24 m/s through 18m of mud, where the resistive force on the car is 17000 N. I don't actually know how to go about doing this, so any pointers in the right direction would be super helpful.
40. ### Total Work versus External Work

Is there an important difference between total work and external work? My knowledge would be that total work a.k.a. net work on a system would be equal to the change in kinetic energy of that system and equal to the line integral of the net force on the system dotted with the differential...
41. ### Determining Work Done by a Person on a Luggage

I'm trying to determine the work done by a person as they pull a luggage up a ramp. The ramp has a height of 5 m and the distance the person walks up is 20 m. The weight of the bag is also 10 kg. I am trying to compare the work done by pulling the luggage up a ramp to carrying an equally heavy...
42. ### Does greater acceleration result in more work done?

Work W done by moving the object with force F for distance s is W = Fs. When I move the same object the same distance but with twice the acceleration, does the work done gets also doubled? By F=ma, doubling the acceleration yields m*2*a = 2F -> 2Fs = 2W. I've mostly read, that if I want to...
43. ### Kinetic energy & Conservation of energy

Homework Statement You are driving with your car (of total mass: 1.2tonnes) with a speed of v=50km/h, until you see an obstacle. a) What is the kinetic energy of the car? b) When you start to brake, there is still 15m until the obstacle. What must be the size of the friction coefficient (µ)...
44. ### Finding the Work of a spring and friction with a changing angle

Homework Statement We shot a projectile with mass ##m## and velocity ##v_0## with angle ##\phi## it collide with a box with mass ##M## at the maximum height of its path. Then, they both start to move with another speed. (We define ##t=0## at this time) (Completely Inelastic Collision). The box...
45. ### Question about the Work-Kinetic Energy Theorem - Pulling a cart

Homework Statement Question from Fundamentals of Physics (Halliday, Resnick, Walker) This figure below shows a cord attached to a cart that can slide along a frictionless horizontal rail aligned along an x axis. The left end of the cord is pulled over a pulley, of negligible mass and friction...
46. ### Speed or turning point using energy

Homework Statement Please look at the attached screenshot. This problem is really confusing for me and I can't seem to make much sense out of it. Homework Equations Ei = Ef The Attempt at a Solution As you can see, I did get (a). (The other checkmarks, I guessed — there were only two...
47. ### I Force fields in curvilinear coordinate systems

I am trying to solve problems where I calculate work do to force along paths in cylindrical and spherical coordinates. I can do almost by rote the problems in Cartesian: given a force ##\vec{F} = f(x,y,z)\hat{x} + g(x,y,z)\hat{y}+ h(x,y,z)\hat{z}## I can parametricize my some curve ##\gamma...
48. ### Find the speed of an object using work and energy

Homework Statement An object with mass 100 kg moved in outer space. When it was at location < 9,-24,-4 > its speed was 3.5 m/s. A single constant force < 250,400,-170 > N acted on the object while the object moved from location < 9,-24,-4 > m to location < 15,-17,-8 > m. Then a different single...
49. ### Calculate the work done moving a crate

Homework Statement you push a box out of a carpeted room and along a hallway with a waxed linoleum floor. While pushing the crate 2 m out of the room you exert a force of 34 N; while pushing it 6 m along the hallway you exert a force of 13 N. To slow it down you exert a force of 40 N through a...
50. ### Can we find work done on this particle, and if not, what are we missing?

Homework Statement A force varies with time according to the expression F=aΔt, where a = 2.0 N/s. From this information, can you determine the work done on a particle that experienced this force over a displacement of 0.50 m? Homework Equations W = F*d Vf = Vo + aΔt F = ma The Attempt at...