What is Work energy: Definition and 186 Discussions

In physics, energy is the quantitative property that must be transferred to a body or physical system to perform work on the body, or to heat it. Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The unit of measurement in the International System of Units (SI) of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of one metre against a force of one newton.
Common forms of energy include the kinetic energy of a moving object, the potential energy stored by an object's position in a force field (gravitational, electric or magnetic), the elastic energy stored by stretching solid objects, the chemical energy released when a fuel burns, the radiant energy carried by light, and the thermal energy due to an object's temperature.
Mass and energy are closely related. Due to mass–energy equivalence, any object that has mass when stationary (called rest mass) also has an equivalent amount of energy whose form is called rest energy, and any additional energy (of any form) acquired by the object above that rest energy will increase the object's total mass just as it increases its total energy. For example, after heating an object, its increase in energy could be measured as a small increase in mass, with a sensitive enough scale.
Living organisms require energy to stay alive, such as the energy humans get from food. Human civilization requires energy to function, which it gets from energy resources such as fossil fuels, nuclear fuel, or renewable energy. The processes of Earth's climate and ecosystem are driven by the radiant energy Earth receives from the Sun and the geothermal energy contained within the earth.

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  1. A

    Work Energy Theorem Loop-The-Loop problem

    http://img530.imageshack.us/img530/5664/looptheloophg9.gif The two problems below are related to a cart of mass M = 500 kg going around a circular loop-the-loop of radius R = 8 m, as shown in the figures. All surfaces are frictionless. In order for the cart to negotiate the loop safely, the...
  2. P

    When do I use the work energy theorem?

    Technically, I don't really have a problem specifically that I need help on solving, but there is a crucial concept that I cannot grasp about the WET, and until I can do so, most WET problems are a pain to me. My professor gave us two types of formulas for the work energy theorem, stating...
  3. T

    Calculating Potential Energy Changes in a Hanging Mass and Glider System

    A samll mass is hanging from an air track system with a mass of 10 grams. It is connected to a glider with a mass of 120 grams. The air track makes on angle of .35 degrees with the horizontal. Assume that the hanging mass and the glider are initially at rest. a) if the mass drops a distance...
  4. A

    Kinetic energy and work energy thereom

    a 5.75 kg object is initially moving so that its x-component of velocity is 6.00m/s and its y-component is -2.00m/s. what is the kinetic energy of the object at this time. What is the change of kinetic energy do that its velocity is 8.50m/s in the x direction and 5.00m/s in the y direction
  5. P

    Calculating Work: Uniform Chain on Table with Hanging Part - IIT 1985

    Homework Statement Uniform chain of length 'L' and mass of 'M' is lying on smooth table and one third of it's length is hanging vertically down over the edge of the table. If 'g' is acceleration due to gravity , then work required to pull the hanging part onto the table is : A)MgL...
  6. P

    Work Required to Pull Chain onto Table (I.I.T 1985)

    Homework Statement Uniform chain of length 'L' and mass of 'M' is lying on smooth table and one third of it's length is hanging vertically down over the edge of the table. If 'g' is acceleration due to gravity , then work required to pull the hanging part onto the table is : A)MgL...
  7. J

    Rotation with Newtons second law and work energy

    Heres the problem http://img141.imageshack.us/img141/2820/49686394mt3.jpg Now I have to work it out using Newtons second law and Work energy... For Newtons second Law (F = ma)...would I be using I = mk^2 M = I\alpha than setting up F = ma...? and for work energy I am...
  8. J

    Work energy incline with spring

    [Heres the Problem... http://i14.photobucket.com/albums/a322/guitaristx/lk.jpg Heres my work so far... http://i14.photobucket.com/albums/a322/guitaristx/Scan10026.jpg Im checking to see if I am headed in the correct direction...
  9. J

    Kinetic Energy and Work Energy Theorem

    A 65kg bicyclist rides his 8.8kg bicycle with a speed of 14m/s. (a) How much work must be done by the brakes to bring the bike and rider to a stop? (b) How far does the bicycle travel if it takes 4.0s to come to rest? (c) What is the magnitude of the braking force? So for part (a) the...
  10. P

    Quick Question - Explain Work Energy Concept

    [Solved] Quick Question - Explain Work Energy Concept Homework Statement Use the work - kinetic energy theorem to find the force required to accelerate an electron (m = 9.11 x 10^-31 kg) from rest to a speed of 1.50 x 10^7 m/s in a distance of .0125 m. Homework Equations W = Fx...
  11. M

    Solving Work Energy Problems: Calculating Distance Using Friction and Velocity

    Homework Statement A 30.0 kg box sliding at 5.00 m/s on a rough surface is brought to rest by 20.0 N of friction. What distance does the box slide? Homework Equations KE = 1/2*m*(v^2-v^2) The Attempt at a Solution I know that the change in velocity is 5.00 m/s since it is going to...
  12. V

    Work Energy Theorem: Delta K Calculation for Particle Moving in x Direction

    A particle moving in the x direction is being acted upon by a net force F(x)=Cx^2, for some constant C. The particle moves from x initial =L to x final=3L. What is Delta K, the change in kinetic energy of the particle during that time? I tried thih by doing the integral of F(x), replacing x...
  13. S

    How Does the Work-Energy Principle Determine the Motion of a Thrown Rock?

    Homework Statement You throw a 25.0N rock into the air from ground level and observe that, when it is 13.0m high, it is traveling upward at 21.0m/s A. Use the work-energy principle to find the rock's speed just as it left the ground. B. Use the work-energy principle to find the maximum...
  14. R

    Work Energy Theorem+Projectile motion

    Homework Statement A 25.0 g mass rests on a 50.0 inclined plane (uk = 0.200). It is pushed against a spring, compressing it 15.0 cm, and released. It moves up the plane and leaves the spring, traveling an additional 45.0 cm before leaving the edge of the plane (at a height of 80.0 cm above...
  15. H

    Work Energy Theorem and speed

    Homework Statement You throw a rock of weight 20.4 N vertically into the air from ground level. You observe that when it is a height 14.9 m above the ground, it is traveling at a speed of 26.0 m/s upward. Use the work-energy theorem to find its speed just as it left the ground; Use the...
  16. J

    Work Energy Problem: Calculating Distance with Friction

    Homework Statement Juana slides a crate along the floor of the moving van. The coefficient of kinetic friction between the crate and the van floor is 0.120. The crate has a mass of 59.1 kg and Juana pushes with a horizontal force of 111 N. If 73.3 J of total work are done on the crate, how...
  17. B

    Need Help with Work Energy Theorem Problem

    I am having some problems, I am on the work energy theorem and I had to do some problems for homework. For one of the questions I was not given enough information. I am supposed to find the initial velocity, when they tell us the final velocity is zero, the coefficient of friction is 0.42...
  18. G

    Physics : Work Energy Power Question

    Homework Statement A bullet of mass 0.0035 kg is shot into a wooden block of mass 0.121 kg. They rise to a final height of 0.547 m as shown. What was the initial speed (in m/s) of the bullet before it hit the block...
  19. M

    How Do You Calculate Work and Distance in These Physics Problems?

    1. A car changes velocity from 25m/s to 8.0m/s. If the average force applied to the brakes is 16000N, how far does the 2300kg car go in this time? 2. How much work is done if a 75kg runner speeds up from 1.2 m/s to 4.0m/s in 1.7s? How much extra work is done if there is a force of friction...
  20. P

    Shooting a block up an incline - work energy

    A block of mass m is placed in a smooth-bored spring gun at the bottom of the incline so that it compresses the spring by an amount x_c. The spring has spring constant k. The incline makes an angle theta with the horizontal and the coefficient of kinetic friction between the block and the...
  21. F

    Work Energy Concept Homework: Solving Statement

    Homework Statement http://xs511.xs.to/xs511/07046/workenergy.JPG Homework Equations The Attempt at a Solution Ok I am all confused on this one. ok so leave part (I) and (II) onto part (III) word done by the pulling force acting on the block = the loss of energy + work...
  22. M

    Work energy theorem force diagram

    I am working on the following problem. Susan's 13.0 kg baby brother Paul sits on a mat. Susan pulls the mat across the floor using a rope that is angled 30 degrees above the floor. The tension is a constant 31.0 N and the coefficient of friction is 0.190 . Use work and energy to find Paul's...
  23. V

    Solving the Work Energy Theorem for an Observer Moving Left

    A 2kg block at rest on a frictionless surface is pulled for 2s by a 10N horizontal force (pull to the right). Use the Work Energy Theorem to determine the final velocity from the perspective of an observer moving to the left. Does the WET still work that observer? I did the calculations...
  24. D

    How Far Will Dave Fall Before the Bungee Cord Stops Him?

    hi i have a Qns. Dave jumps off a bridge with a bungee cord( a stretchable cord) tied around his ankle. He falls for 15m before the bungee cord begins to stretch. Dave's mass is 75kg and we assume the cord obeys Hook's law with elastic constant, k= 50N/m. if we neglect air resistance and the...
  25. S

    What Are the Units of Constant C in a Force Equation?

    Ok I need this answered by whoever can. The force on an object is F=C/x^2 A) what are the units of C? b)How much work is done by this force when the object is moved from x=a to x=3a. How much work is done by F when the object is moved from x=3a to x=infinite units of x are in meters I...
  26. J

    Solving Work, Energy & Friction for Block Movement & Spring Compression

    Just need a simple logic check here. Let's say a block of 2kg is positioned on an incline of 53 degrees. 4m from the block is a spring with a k=70N/m. the coefficient of kinetic friction is 0.36. How fast is the block moving when it hits the spring? How far is the spring compressed. Ok, so...
  27. R

    Work Energy Theorem in Moving reference frames

    This is a highly theoretical question... so beware! The Work Energy(WE) equation in Mechanics says that the net total work done on an object due to various conservative and non-conservative forces equals the change in kinetic energy of the body. This above theorem is usually derived simply from...
  28. T

    Work, Energy & Motion: Connecting the Concepts

    Here's a simple question that I get confused in explaining.. Can work be done on something if there is no motion? This was a test question...and of course I wasn't thinking clearly..and I said that work can be done since motion is relative to something, work can be done... I thought, for...
  29. W

    Solve Work Energy Problem: Calculate Velocity v at B

    I'm confused about this problem. (a diagram is included below).. The 0.5 kg collar slides with negligible friction along the fixed spiral rod, which lies in the vertical plane. The rod has the shape of the spiral r = 0.3\theta, where r is in meters and \theta is in radians. The collar is...
  30. D

    Work Energy Theorem and kinetic energy

    The work energy theorem says that ''The work done by the net force acting on a body results change only in its kinetic energy. '' But if the resultant force is in vertically up direction it will surely change its potential energy too, so what's the solution here.
  31. C

    Work energy method and impulse momentum method

    we have two concepts 1)if force is applied for a distance x(i.e work) it increases the kinetic energy of a mass 2)if force is applied for a time t(i.e impulse) it increases the momentum of the mass why there are two concepts. Are the above two same?
  32. marlon

    Newtonian Mechanics, Motion on Inclines, Work Energy Theorem

    Let's start with the very base of Newtonian mechanics. It works like this : Suppose we work in two dimensions denoted by a x-axis and an y-axis. You can work in as many dimensions as you want because all you have to do is add a unit vector to the formula's, as you will see. Starting from the...
  33. F

    Work energy theorem problems cracking my heard

    Hello members Please could you help me with solutions for the following two problems that I am stuck with. King Kong is capable of jumping to a maximum vertical height of 10 m. He picks up Enrico Fermi, who is exactly 10% of Kong's mass, and leaps upwards. To what maximum height can King...
  34. N

    Solve Work Energy Problem: Find Theta for Skier on Slope

    A skier slides down a slope 10.2m long, inclined at an angle (theta) to the horizontal. The coefficient of kinetic friction is 0.11. Skier's initial speed is 1.9m/s and final speed at the bottom of the slope is 8.3m/s. Find (theta), air resistance is negligible. I have applied F=ma and...
  35. A

    Solve Work Energy Problems: Questions & Answers

    Well i am taking physics cp so these problems should be fairly easy but I've been sitting here for about an hour and somehow i am still drawing a blank. I did these problems with ease last week but somehow i am utterly dumbfounded now without the slightest hint on how to do these. I think i am...
  36. L

    Work Energy Theorem Question I cant do

    I have no clue how to do b, c and especially d. Thanks The cable of the 1,800 kg elevator cab in Fig. 8-51 snaps when the cab is at rest at the first floor, where the cab bottom is a distance d = 3.9 m above a cushioning spring whose spring constant is k = 0.14 MN/m. A safety device clamps...
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