work done Definition and Topics - 61 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:



{\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. M

    Work done on moving a submerged object

    I first worked out the buoyant force using rho = 1000, g = 9.8 and V = 1. (this gives Fb = 9800) I then worked out Fg of the tank (5 x 9.8 = 49) Then I used Fnet = Fb - Fg - T = 0 to work out tension as 9751. I thought the work done would be the work done by tension (9751 x 50.4), but I'm not...
  2. T

    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...
  3. 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...
  4. brotherbobby

    Work done on a conical pendulum

    The diagram for the problem is shown alongside. In the vertical (##\hat z##) direction we have ##T \cos \theta = mg##. In the plane of the pendulum, if we take the pendulum bob at the left extreme end as shown in the diagram, we have ##T \sin \theta = \frac{mv^2}{r}## (the ##\hat x## axis of...
  5. Adesh

    Why the work done is coming out to be positive?

    In textbooks or in lectures it is said that : Work can be either positive or negative: if the force has a component in the same direction as the displacement of the object, the force is doing positive work. If the force has a component in the direction opposite to the displacement, the force...
  6. Adesh

    A proof that magnetic forces do no work?

    The proof of magnetic forces do no work is given in Introduction to Electrodynamics by David J. Griffiths like this My problem is why he has replaced d\mathbf{l} with \mathbf{v}dt? This substitution implies that the charged particle was moving with \mathbf{v} only and no force acted on it...
  7. T

    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...
  8. SLTH02

    Work required to attach the bowstring to the bow?

    E final = (1/2)(500)(1.14012)^2 = 324.968 J E initial = (1/2)(500)(0.5)^2 = 62.5 J E final - E initial = 262.468 J
  9. weilam06

    Work done by an electric motor to drive elevator

    For the part (a), set the tension of the string that pulls the elevator be ##T_1## and the tension that pushes the counterweight be ##T_2##. Then we have the following equations: $$T_1−1200g=1200 \cdot 1.5$$ $$1000g−T_2=1000 \cdot (−1.5)$$ where ##g=9.8 ms^{−2}## stands for gravitational...
  10. Hawkingo

    Why there is a negative sign in the formula of calculating work done?

    $$W = - \int _ { a } ^ { b } \vec { F } \cdot d \vec { r }$$ ( The Force here is referring to the applied force, When moving a positive charge towards another positive charge(stationary) / field In this formula why there is a negative sign in the formula? I am not asking the sign of the total...
  11. Hawkingo

    Why the work done is negative when bringing 2 opposite charges together?

    we know that if the applied force is in the direction of the displacement then work done is positive.But in case of bringing 2 opposite charges from infinite to a certain distance,the work done is negative even the force and the displacement of the charge is in the same direction. From...
  12. D

    Definitions for work done

    Are the following definitions correct? Work done as energy transferred The energy transferred when the forces between two objects interact Work done by a force Work done = force x distance moved in the direction of force applied (W=F*Δs) Work done by a gas Work done = pressure x change...
  13. A

    How much work needs to be done on a piano to move it into the bed of 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...
  14. 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...
  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. 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...
  17. 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...
  18. 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...
  19. 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...
  20. A

    Work Done at an angle

    Homework Statement What is the minimum work needed to push a 1000-kg car 300 m up a 17.5 degree incline? A. Ignore friction B. Assume the coefficient of friction is 0.25 Homework Equations W = F*d Net force = ma The Attempt at a Solution At first I did: Work = F*300*cos17.6 but I later...
  21. A

    Work and Kinetic Energy

    Homework Statement This is a lab I did for physics. In this experiment, a glider starting from rest on an air track is attached to a string. The string is drawn over a pulley with a mass hanger tied to the other end. Work is done by gravity which results in a gain of kinetic energy of the...
  22. A

    What should be the work done here?

    Homework Statement If you apply a force F with the x component =-6.97 N and the y component = 8.47 N on a car which moves along the x axis by a displacement of 3.37m. What is the work done on the car by your force in J? Homework Equations W=Fxd The Attempt at a Solution I think that the...
  23. Nikhil Rajagopalan

    Work done by Static friction

    Friction is said to be a non conservative force. And I see various sources state that work done by a non conservative force on a round trip is always non zero. But is that always true? In a case where a coin is placed on a turn table, and the table is rotated, and the coin does not move during...
  24. hackhard

    Work done by voltage source

    Is the work done by a constant voltage source positive or negative when current is opposite to emf?
  25. R

    Change in internal energy when water is heated from 0 to 4c

    Homework Statement : [/B]Find the change in internal energy of 2kg water as it is heated from 0°C to 4°C. The specific heat capacity of water is 4200J/Kg and its densities at 0°C and 4°C are 999.9 kg/m3 and 1000kg/m3 respectively. Atm pressure=105Pa Homework Equations :ΔU= Q-W W=PΔV M/V=D[/B]...
  26. Nikhil Rajagopalan

    Work done by internal forces on a system of particles

    Dear Experts, Trying to analyze the work done by internal forces in a very simple two particle system which is attracted to each other with a constant force, i performed calculations based on two frame of references, 1.The center or mass frame of reference and 2. Frame of reference of one of the...
  27. M

    Work done on brakes vs kinetic energy lost by vehicle

    When doing work on the brakes of a car or bicycle, how much of that energy is actually removed from the total kinetic energy of the vehicle? What is the most efficient braking system?
  28. L

    Calculate area of PV diagram. Two isotherms, two isobars

    Homework Statement Everything is in attached file. Given the PV diagram with P2, P1, V2, V1. Homework Equations PV=nRT W=nRT*ln(Vf/Vi) The Attempt at a Solution Attempt in attached file is very organized. I showed 2 of my peers and they are getting the same answer as well. Anybody have any...
  29. Ian Baughman

    Thermodynamic Process

    What is wrong with this logic, if any? It does not seem like this should be true but maybe I'm mistaken. Assuming the process consists of two isobaric processes and two isothermal processes the work from B to C in terms of p1, p2, V1, and V2 is given by the following. 1) WBC=p2(VC-VB) 2)...
  30. S

    Finding the total mechanical energy

    Homework Statement A bead is sliding on a surface. At point A it is 80 cm above the ground, at point B it has just hit the ground and at point C it is 50 cm above the ground. At point A it has a speed of 200 m/s, so what will its speed be at point B and C? Homework Equations W=F.d Kinetic...