Work done Definition and 1000 Threads

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. kolleamm

    Work done by a force on a spring

    Homework Statement The unstretched length of a spring with 'k' = 250 N/m is 20 cm. A force 'F' is applied to stretch it to a length of 24 cm. How much work was done by 'F'? Answer : 0.2 Nm Homework Equations F = k * delta x Work = F * delta x The Attempt at a Solution [/B] change in spring...
  2. shahrilmajid

    Finding work done by worker pulls

    Homework Statement Homework Equations fd cos theta The Attempt at a Solution Finding the work done. Please anybody help me[/B]
  3. A

    Work Required to Move a Piano Onto a Truck

    Homework Statement Movers must push a piano onto a truck, the bed of which is a height 1.35 m above the ground. To do this they will use a frictionless ramp. If the piano has a mass of 1806.0 kg and the movers push it up the slope at a constant velocity, how much work do they need to do on it...
  4. S

    Curious about Work done by Gravitational force

    Homework Statement I don’t understand why this would relate to cosine and not sine, if gravity is often assiciated in the up and down part of a free body diagram. Homework Equations Wg=mgdcos(theta)[/B]The Attempt at a Solution Is it because it would depend on your reference frame?
  5. S

    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...
  6. arturo

    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 a...
  7. L

    Work done when Inserting a Dielectric between Capacitor Plates

    Hi, today in lecture, we discussed the work done on inserting a dielectric between a capacitor. Two cases of this example: One case, where the battery is disconnected so that the charge stays constant. Other case where the battery stays connected so voltage is constant. I am confused on...
  8. C

    The concept of a force lifting a weight and the work done

    if I apply a force constant F=100N en ##y## direction to a body of mass 2kg, it is elevated 3m and I know that the force of gravity is in ##y## direction too. What is the work that I did? I think: ##W_{me}=(F_{me}-F_{g})\times 3## it is correct? and the work made by gravity is "0".
  9. P

    Finding the Coefficient of Friction in a Spring-Block Incline System

    Hi - I'm looking for some help with the solution of this problem "A 1 kg block situated on a rough incline is connected to a spring with spring constant 100 Nm-1 as shown in Figure. The block is released from rest with the spring in the unstretched position. The block moves 10 cm down the...
  10. P

    How Much Energy Does a Dieter Use by Lifting Weights?

    Hi - Question: A person trying to lose weight (dieter) lifts a 10 kg mass, one thousand times, to a height of 0.5 m each time. Assume that the potential energy lost each time she lowers the mass is dissipated. (a) How much work does she do against the gravitational force ? (b) Fat supplies 3.8...
  11. giveortake

    Calculating the work done from an equation for variable force

    Homework Statement The force on a particle is directed along an x axis and given by F = F0(x/x0 - 1) where x is in meters and F is in Newtons. If F0 = 1.5 N and x0 = 4.9 m, find the work done by the force in moving the particle from x = 0 to x = 2x0 m. Homework Equations F = force, w = work, x...
  12. S

    Work done by Octane Combustion Engine

    Homework Statement There is an insulated internal combustion engine fueled by one mole of octane. It operates at a constant pressure of 5.0 bar. The initial temperature is 200°C. Calculate the heat exchanged with the surroundings, the Δh for the gas, the final temperature, the work performed...
  13. almarpa

    Morin's explanation about the work done by friction

    Hello all. In his books on classical mechanics, David Morin claims that when computing the work W = F Δx done by a contact force that don’t involve any slipping, we can equivalently say that Δx is the displacement of the thing that is applying the force. Later, when analysing a wheel rolling...
  14. S

    How Is Work Calculated for a Gas and Balloon in Isothermal Expansion?

    Homework Statement The question is: One kilogram of a gas with a molecular weight of 35 is contained in a balloon. The initial conditions are 27 C and 0.025 m^3. The gas is slowly heated isothermally until the final volume is 0.05m^3. The atmospheric conditions are 100 kPa and 27 C. The p-v-T...
  15. shihab-kol

    Work done in adiabatic process vs work done in isothermal

    Homework Statement [/B] An ideal gas is compressed to the same volume from the same initial state for both an adiabatic and an isothermal process. In which case will more work be done ? 2. Homework Equations ##dU=dQ - dW ## ##W=\int P\,dV ##(For isothermal) ##W=nc_vdT##...
  16. T

    Confusion about the work done by an ideal gas

    When an ideal gas,in a piston kind of system and whose equilibrium state is mentioned, is allowed to expand (piston is allowed to move and not gas leaking )against a constant external pressure very quickly, then, is the work done by gas zero or not zero ? The argument for work being zero is...
  17. navneet9431

    Intuitive explanation of why work done by tension is 0?

    Homework Statement Homework Equations Work Done=Force*Displacement in the direction of the force The Attempt at a Solution I tried to solve the problem this way, I wrote these equations for the two masses, T-mg=ma...(i) Mg-T=Ma...(ii) From (i)&(ii), T=[M(g-a)+m(a+g)]/2 and then I would...
  18. navneet9431

    Problem in calculating work done?

    Homework Statement See question number 3 Homework Equations Work Done="integral" F*ds The Attempt at a Solution I tried to solve this question using integration, I have replaced F with "1" and ds with "t^2+2t". So I am stuck in at that step. Please help me differentiate it further or solve...
  19. navneet9431

    Calculation of work done by a variable force

    Homework Statement See the explanation of work done by variable forces given in my textbook. For calculation of work done by variable forces the author analyses only a small fraction of displacement "ds". And then he makes **assumption** that the force is acting on the particle at an angle...
  20. N

    Work done under constant velocity

    Depending on the answer to this question, I may have others. Consider a one-dimensional ice rink. Rightwards is taken as the +x direction. A box of mass m slides leftward on the surface with a constant velocity v. Two people go to opposite ends of the box and apply equal and opposing forces...
  21. Bennett Haselton

    Use internal pressure to compute work done by an expanding gas?

    I would argue that if you are computing the work done by an expanding gas in a frictionless piston, in an irreversible expansion where the inner pressure is greater at all times than the (constant) outer pressure, that you should integrate the internal pressure over volume change, not multiply...
  22. A

    Thermodynamics, find the work done from the graph

    Homework Statement Using the data presented in the accompanying pressure-versus-volume graph, estimate the work done (including the algerbraic sign) when the system changes from A to B to C along the path shown. Homework Equations The work done is the area from change in position and time...
  23. M

    Are flow work and work done during isobaric expansion similar?

    In case of isobaric expansion, the system expands at constant pressure(the external pressure i.e. the resistance is constant.).In case of flow work, the fluid trying to exit the control volume, pushes against the pressure at the exit of the control volume or when entering the control volume, the...
  24. C

    Work done per unit charge by electric field on charge

    Homework Statement Homework EquationsThe Attempt at a Solution I know the units for V is J/C so #3 and #4 are wrong. But how do I determine the signs?
  25. Decimal

    Work done in reversible and irreversible processes

    Hello, I am encountering some confusion understanding the difference in working with reversible and irreversible processes in thermodynamics. Let's say I have a process where an ideal gas at a certain starting temperature ##T_i## expands from volume ##V_i## to ##V_f##. The temperature of the...
  26. isukatphysics69

    Find the work done by the spring force on a box

    Homework Statement Homework EquationsThe Attempt at a Solution Wspring = ∫-k*xdx limits of integration are 12 and 0 So [0 - .12^2/2]*172 = -1.24J of force Getting 1.8/2 points for this anser
  27. P

    Determine the work done by the force due to gravity

    Homework Statement If the height of a frictionless incline is h. Determine the work done by the force due to gravity F as the crate of the mass m slides down the incline Homework Equations W=Fd cos (theta ) Force due to gravity perpendicular to incline= mg cos(theta) The Attempt at a...
  28. F

    The work done by the electric field between two plates

    Homework Statement Homework Equations ##V=Ed## ##ΔU=ΔV Q## The Attempt at a Solution Since the electric field is constant between charged plate conductors , d and the potential difference (ΔV) don't change.So, the potential energy (ΔU) remain the same . The answer is (C). Right ?
  29. H

    Work done for isothermal process in terms of Helmholtz func

    The Helmholtz function differential form for a reversible process is: dF = -SdT - PdV, as for a reversible process δW (by system/here an (ideal) gas) = PdV and dS = δQ/T. Therefore, for a reversible isothermal process, dT = 0 and hence dF = -PdV. Therefore, the work done by the system is W =...
  30. L

    About the total work done loading and unloading (setting down) an object

    The other day I saw this question: "A man carries a suitcase weighing 50kg over his head, and travels a distance of 15m along a horizontal direction. What would be the work done?" My answer was: "Suposse the height of the man is 1.8m. Then, the work done by the man, considering the...
  31. K

    Given a uniform chain on an incline, find the work done by friction

    Homework Statement A uniform chain of mass 'm' and length 'l' rests on a rough incline (inclination is angle 'Q') with its part hanging vertically. The chain (inclined) starts moving up the incline (and the vertical part moving down) provided the hanging (vertical) part equals to 'n' times...
  32. J

    Work done by friction on smaller block

    Homework Statement Homework EquationsThe Attempt at a Solution If the two blocks were to move together when the external force of magnitude mg is applied , the acceleration would be mg/3m = g/3 . This acceleration would have to be provided by friction . Value of friction should be mg/3 . But...
  33. M

    Calculating work done by a Carnot engine

    "A Carnot engine operates using a heat source at 500 °C, and a heat sink at room temperature (20 °C). Suppose that as a heat source, you use the combustion of 100 cubic feet of natural gas at room temperature and pressure (e.g. in a fuel cell of some kind). Under ideal conditions, what is the...
  34. Grands

    How important is the work done by people who work in finance?

    Hi guys. Due to the reason that I do not have a great knowledge related to finance, I wanted to ask if someone can simply explain me how important is for the society, the work of the people that work in the finance. How their job is useful for the people? Thanks Grands.
  35. Pushoam

    Work done in a thermodynamic process

    Homework Statement Homework EquationsThe Attempt at a Solution The work done is maximum in the path (3) as the area covered by this path is maximum. Now, dU = dQ + dW, the work done is minimum in the Path (1) , so dQ should be maximum. Hence, the correct options are A and C. Is this correct?
  36. G

    Which Gas Compression Process Requires the Most Work?

    Homework Statement This is a conceptual question. An ideal gas is compressed to half its initial volume by means of several possible processes. Which of the following processes results in the most work done on the gas? a) isothermal b) adiabatic c) isobaric d) The work done is independent of...
  37. A

    Confusion regarding Electric Potential Energy and Work

    Hi everyone. I've been doing a lot of reading regarding electric potential and electric potential energy. Unfortunately, I have a lot of confusion regarding this topic, as I keep receiving different information. My main confusion is regarding the signs, positive or negative, of work and it's...
  38. H

    Find the work done on a monoatomic gas in this P-V diagram

    Homework Statement Homework Equations internal change = $$\frac{3}{2}n.R.(T2 - T1)$$ Work = P.ΔV The Attempt at a Solution 1) T2 = $$\frac {P2. V2 . T1 }{P1 . V1} = 1.2 * 10^3$$ 2) Q = Internal change = $$\frac{3}{2}n.R.(T2 - T1) $$ $$ = \frac{3}{2} * 1 *8.3*10^{-3}*(12*10^2 - 3*10^2) $$...
  39. D

    Understanding Work Components in Calculating Net Work Done

    Homework Statement Homework Equations The Attempt at a Solution I do not understand why is mgh2 is being subtracted from the overall equation instead of added. I am able to construct each of the work components but when building the overall equation I'm having a problem of understanding...
  40. Pushoam

    Maximum work done by a Carnot engine

    Homework Statement Homework EquationsThe Attempt at a SolutionTaking the engine to be a Carnot engine, ## \eta = \frac { T_h – T_c } {T_h} = \frac { W} {Q_h} ## ...(1) ## Q_h = C(T_h – T_f) ...(2) \\ Q_c = C(T_f – T_c) ...(3) \\ W = Q_h – Q_c = C(T_h + T_c – 2 T_f) ## ...(4)Solving...
  41. M

    Work done by the system, positive or negative?

    My chemistry course says that work done by the system is negative, but physics course says that work done by the system is positive, I'm sure I'm missing something and I really need to understand it. Thanks.
  42. K

    Work done by the force of a man on a crate of 80N

    Homework Statement A man pushes an 80-N crate a distance of 5.0 m upward along a frictionless slope that makes an angle of 30° with the horizontal. His force is parallel to the slope. If the speed of the crate decreases at a rate of 1.5 m/s2 , then the work done by the man is: (a) –200 J (b) 61...
  43. axer

    Work Done by Gravity - Positive or Negative

    Homework Statement Homework EquationsThe Attempt at a Solution I first said it's B, since force throws up = positive. gravity down= also positive, please help asap thanks
  44. Alexanddros81

    Derive the expression for the work done by the friction force

    Homework Statement 14.6 The coefficient of kinetic friction between the slider and the rod is μ, and the free length of the spring is ##L_0 = b##. Derive the expression for the work done by the friction force on the slider as it moves from A to B. Neglect the weight of the slider. Homework...
  45. Alexanddros81

    Derive the expression for the work done by the ideal spring

    Homework Statement Derive the expression for the work done by the ideal spring on the slider when the slider moves from A to B. Assume that the free length of the spring is (a) ##L_0 = b##; and (b) ##L_0 = 0.75b## Homework EquationsThe Attempt at a Solution Can you check if my solution...
  46. S

    What Must Remain Constant for W = pΔV to Apply?

    Homework Statement The work done W by an expanding gas is calculated using W = pΔV. What must remain constant for this equation to be used? a. The pressure of the expanding gas b. The pressure of the surroundings c. The temperature of the expanding gas d. The temperature of the surroundings e...
  47. JHLee

    Calculating Tension Using Work Energy Theorem

    Hi, I have a homework and I kind of stuck on it. Here is the question: A 17 kg object on a rough ramp (coefficient of friction = 0.35N, ramp's angle = 25 degrees) is connected to a vertically hanging object via a pulley with I = 23 kg m^2 and the radius is 0.25m. The hanging object had weight...
  48. A

    External Forces and Potential Difference

    Homework Statement The work done by an external force to move a -8.0 uC charge from point a to point b is 25*10^-4 Joules. If the charge was started from rest and had 5.2 * 10^-4 Joules of kinetic energy when it reached point b, what must be the potential difference between a and b? Homework...
  49. V

    Work done in expansion of a bubble

    Homework Statement as title Homework Equations force exerted by atmosphere on bubble = 2(on account of dual layer) * 2pi*r*L(surface tension) work is the integral of force *dx The Attempt at a Solution so we're looking at int ( 4pi*r*L *dr) but since not it 1 particle is traveling against...
  50. A

    Negative work and electric potential energy

    I am confused how a charge could have negative work done. To clarify, I was doing a problem earlier in which a positive charge and negative charge are moving towards each other. I used the equation work = Δv * q And when I was doing this, the change in electric potential, Δv, was negative, and...
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