# What is Work energy: Definition + 187 Threads

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. ### B Curious about the work - energy theorem

I'm sorry my question seems too strange. The work done by a net force is equal to the change in the kinetic energy of an object.This is very simple, but I suddenly encountered a confusing problem. If you hang an object on a weightless string and apply a force of 10N in a straight line, moving...
2. M

### Work energy KE theorem for a book being lifted up in a gravitional field

For this, From the work kinetic energy theorem, if we assume that the book and the earth is the system, and that the finial and inital speed of the system is zero, then is the work KE theorem there is no net work done on the system. However, clearly there is work done on the system is shown by...
3. ### Why does the logic of negative acceleration not always indicate negative work?

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...
4. ### I Bernoulli's equation and the work energy theorem

Hello physics researchers, teachers and enthusiasts. I notice one little thing is confusing me in the derivation of Bernoulli's equation in the article, they write:$$dW = dK + dU$$where dW is the work done to the fluid, dK is the change in kinetic energy of the fluid, and dU is the change in...
5. ### B Work energy theorem by variable force

Its Good to be Back! From Resnik, Fundamentals of physics: Consider a particle of mass m, moving along an x-axis and acted on by a net force F(x) that is directed along that axis. The work done on the particle by this force as the particle moves from position ##x_i## to position ##x_f## is given...
6. ### MHB Work energy principle and power

Particle X of mass 2 kg , and particle Y of mass m kg are attached to the ends of a light inextensible string of length 4.8m. The string passes over a fixed smooth pulley and hangs vertically either side of the pulley. Particle X is held at ground level, 3m below the pulley. Particle X is...
7. ### MHB Work energy principle and power

A car of mass 1200 kg accelerates up a hill inclined at 10 degree to the horizontal. The car has initial speed of 10 m/ s and final speed of 12 m/s after 60 s. Air resistance and friction may be ignored. Find the average power generated by the engine. The and in the textbook is 36000 W, iam...
8. ### MHB Work energy principle and power

A golf ball of mass 45.9g is hit from a tee with speed 180km/ h. The ball rises to a height of 20m having traveled along a curved path of length 61.875m. At the highest point of its path the ball is traveling at 144 km/h a) Find the magnitude of the avg resistance force acting on the golf ball...
9. ### MHB Work energy principle and power

A golf ball of mass 45.9g is hit from a tee with speed 50 m/ s. The ball lands in a pond 5m lower than the tee. When the ball lands in the pond it has traveled a curved path of length 160m. The resistance acting on the ball has magnitude 0.3N a) Find the speed of the ball just before it hits the...
10. ### MHB Work energy principle and power

A sky diver of mass 80 kg falls 1000m from rest and then opens his parachute for the remaining 2000m of his fall. Air resistance is negligible until the parachute opens. The sky diver is traveling at 5 m/ s just before he hits the ground. Find the average resistance force when the sky diver is...
11. ### MHB Work energy principle and power

A football is kicked from the ground level with speed 15m/s and rises to a height of 1.45m. Assume that air resistance is negligible a) Find the speed of the ball when it is 1m above the ground Increase in GPE= loss of KE mgh=1/2mu^2-1/2mv2 10×(1.45-1)= 1/2×15^2-v^2/2 V= 14.7 m/ s But textbook...
12. ### MHB Work energy principle and power

A box slides down a smooth ramp. The height of the ramp is 20cm and the length of the ramp is 2.5m. The box starts from rest. What is the speed of the box when it reaches the bottom of the ramp? I don't understand how to solve this. Pls help
13. ### MHB Work energy principle and power

A child of mass 40kg slides down a playground slide. The child starts from rest at the top of the slide, 2m above the ground. At the bottom of the slide it's slope levels off. a) Find the child's loss of GPE I got the ans 800J there is a constant resistance of 112N throughout b) find the...
14. ### MHB Work energy principle and power

A girl of mass 50 kg travels down a water slide. She starts at the top with a speed of 2 m/s and descends through a vertical height of 5m. a) Assuming that there is no resistance, find her speed when she reaches the bottom of the slide I got the ans 10.2m/ s b) the girl's actual final speed is...
15. ### MHB The work energy principle and power

A box of mass 25kg is pulled 5m across a smooth floor by rope with tension 22N. The rope is inclined at 40 degree to above the horizontal. There is a frictional force with average value 12N. The box starts from rest. Find the final speed. Iam getting the ans 1.97m/s. The textbook ans is 1.39 m/s...
16. ### Work and Energy on a Slope - How Does a Block Move Up with Zero Net Work?

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...
17. ### 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...
18. E

### Is conservation of energy derived from the work energy theorem?

To my mind, there are two distinct approaches to energy problems that different authors tend to use, and I wondered whether either is more fundamental than the other. The first is variations on the work energy theorem, and the second consists of defining a system boundary and setting the change...
19. ### Work-Energy Theorem: Is Lifting a Rigid Body Really 0 Work?

I read on the Internet that the work done by a (rigid) body = the change in Kinetic energy. What if I lift a rigid body slowly and vertically by 1 meter above the Earth's surface so that the initial velocity = final velocity =0? According to the Work Energy theorem as stated on many sites on...
20. ### Work done by friction on a two-block system

I calculated friction = 1N.But since force is more than maximum friction,therefore lower block will not move and a force of 0.5N will be applied to upper block. Therefore its work done by friction will be W=0.5×6=3 J. But answer given is 1 J. Can anyone help.
21. ### Not sure how to plug in numbers for Work Energy Theorem

1. The Problem Stament, all variables and given data a 15 kg crate, initially at rest, slides down a ramp 2.0 m long and inclined at an angle of 20 degrees with the horizontal. if there is a constant force of kinetic friction of 25 N between the crate and ramp, what kinetic energy would the...
22. ### Question about work energy theorem

Homework Statement Homework EquationsThe Attempt at a Solution I don't know how to do part 5, I know the point of maximum speed is at an angle of 120 degrees because the work starts to be negative, but how do I find of the maximum speed at that point without using vector integration? (I...
23. B

### Non-conservative work energy theorem and potential energy

Here is problem I quickly made up: Suppose there is a ramp with a height of 6 meters and length of 12 meters. A block of 5 kg is pushed up to the top of the ramp with a constant velocity. The force of friction is 15 N. Here's the confusion: By using the non-conservative force work energy...
24. B

### Question about work energy theorem

Hello, I am confused about the work energy theorem. If someone goes up the stairs at a constant velocity, is work being done on the person? After all, Wnet = change in kinetic energy, and that change is zero. This is the original problem that I am trying to solve, from David Morin's Problems...
25. ### Does work energy theorem fail while dealing with friction?

Let's consider a setup consisting of a table with friction, and a block on top of it. Suppose we drag the block across the table with a constant speed. The applied force ##f_{app}## acting through a distance ##d## does a work ##f_{app}d##. The frictional force ##\mu N## is equal to ##f_{app}##...
26. S

### Work energy theorem and forces at equilibrium -- Conceptual doubt

A pendulum of mass m and length l is suspended from the ceiling of a trolley which has a constant acceleration a. Find the maximum deflection θ of the pendulum from the vertical. When I used work energy theorem, I got θ = 2 arctan(a/g). But when I took the equilibrium position and equated the...
27. ### Work Energy Theorem: particle, system of particles, rigid body

Question: A) Derive the work - energy theorem for one particle. B) Check whether it is applicable for a system of particles and a rigid bodyWork - energy theorem for one particle system, total sum of work done by individual forces = work done by total force To show the above equality, let's...
28. ### Work Energy Equation Help (what size shock absorber to use)

Hi everyone. I'm trying to work out what size shock absorber to use. It's going under a seat so just the weight of a man really that it has to support. I've found a website showing the equations I need but I'm not sure about one of the steps. In step 2 it asks force output of the motor/drive...
29. ### B Need a bit more clarification on W=F.ds

I was a bit confused about the work energy theorem. I perfectly understood it's applications for point sized particles but I'm a bit confused about its application on extended bodies both rigid and non rigid. Case 1 {for rigid bodies} :- Consider a rod of definite mass hinged at the top. It's...
30. ### Why Ignore Tension In Pulley and Work Energy Problems?

A pulley and block system is a favorite type of system for analysis when considering work-energy problems in beginning dynamics. It's commonly recommended that the best approach to the system is to write an equation for the whole system, while ignoring the work done by cables/ropes and focusing...
31. ### Spring problem using work energy theorem

Homework Statement A 2.90 kg block on a horizontal floor is attached to a horizontal spring that is initially compressed 0.0360 m . The spring has force constant 860 N/m . The coefficient of kinetic friction between the floor and the block is 0.35 . The block and spring are released from rest...
32. ### Using Work Energy Theorem to Find Necessary Velocity

1. The problem statement, all variables and given/ You must push a box up an incline plane (the angle being constant : a), to a person waiting to receive it, who is a distance of h(constant) vertically above you. Though the slope is slippery, there is a small amount of friction with kinetic...
33. ### Energy change of reservoir in reversible weight process

In what follows I refer to the ideas of "Thermodynamic: Foundations and Applications" by Gyftoploulos and Beretta. The abbreviated form of my question is: In a reversible weight process, Ω1R-Ω2R = E1 - E2 (see eqn. 6.18, p. 99) is transferred out of the composite of a system A and a reservoir R...
34. ### Applying work energy theorem to unifrom circular motion

Homework Statement attempt to derive the equation of centripetal acceleration using work energy theorem Homework Equations work done = Change in kinetic energy The Attempt at a Solution consider diametrically opposed points occurring in uniform circular motion - displacement = 2*R and let...
35. ### Question on work energy and power kinetic energy of an ....

Homework Statement If the speed of a vehicle increases by 2m/s then it's kinetic energy is doubled. Find out the original speed of the vehicle Homework Equations 1/2(mv^2) The Attempt at a Solution First find out both KE(kinetic energy) taking u(initial vel.) And v(final vel.) And mass as m...
36. ### How Do You Calculate Energy and Speed on a Roller Coaster?

Homework Statement Ima Scaarred (m=56.2 kg) is traveling at a speed of 12.8 m/s at the top of a 19.5-m high roller coaster loop. a. Determine Ima's kinetic energy at the top of the loop. b. Determine Ima's potential energy at the top of the loop. c. Assuming negligible losses of energy due to...
37. ### How Long Will it Take to Heat Water Using a Solar Heater?

Homework Statement A solar heater is used to warm 150 kg of water by 30 K. The intensity of solar radiation is 6000 Wm-2 and the area of the panels is 4.0 m2. The specific heat capacity of the water is 4.2 * 103 J/kg/K. Estimate the time this will take, assuming a solar panel efficiency of...
38. ### Please help me with this mechanics problem -- pulling one end of a spring

Homework Statement A spring of unstretched length l has a mass m with one end fixed to a rigid support. Assuming spring to be made of a uniform wire, the kinetic energy possessed by it if its free end is pulled with uniform velocity v is? 2. Homework Equations potential energy stored in a...
39. ### Work that must be done to charge a spherical shell

1. Calculate the work that must be done on charges brought from infinity to charge a spherical shell of radius R = 0.100 m to a total charge of Q = 125 μC.2. V = k_e\int{\frac{dq}{r}} \triangle V = - \int{E \cdot ds} W = q\triangle V 3. I started with assuming the spherical shell produces an...
40. ### Work on 1 pulley system and two masses

Homework Statement this is from an example problem in the hibbler dynamics book 13th edition in the section of work so i don't really have a question on how to do it. the question is why is the problem solved the way it is solved. the system has one pulley.one rope.and two masses at each end...
41. ### Work Energy Theorem in Spring Block System

Just got confused that while applying the Work - Energy Theorem in a vertical Spring-Block system performing SHM (considering no other external forces other than gravity), when I apply the theorem from equilibrium position, do I consider the work done by gravity?
42. ### Work Energy and deflection Problem

Homework Statement The 2 kg piece of putty is dropped 2m onto the 18 kg block initially at rest on the two springs, each with a stiffness k =1.2kN/m . Calculate the additional deflection of the springs due to the impact of the putty, which adheres to the block upon contact. Homework Equations...
43. ### Can the Work-Energy Theorem Determine Speed for Variable Acceleration?

1. Homework Statement The Attempt at a Solution I was wondering if I did something wrong for the 50m. I did the same process of finding the area under the line. I'm assuming it's possible to get the same speed since the net work is the same.[/B]
44. ### How Does the Work-Energy Theorem Apply to a Slipping Chain?

Homework Statement A uniform chain of mass m and length l overhangs on a smooth table with two third part lying on the table. Find the kinetic energy of the chain after it slips off the table. Homework Equations F=ma Total work done by all forces = change in kinetic energy The Attempt at a...
45. ### Simple Work Energy Principle Question

I think I did most of this question correctly, but I think I might be overlooking a few steps because I might have thought about it too simply. A dinner plate of mass 510 g is pushed 60 cm along a dining table by a constant force of 3.0 N directed 22° below the horizontal. If the coefficient...
46. ### Solving for Block A's velocity: Va = 3.8 m/sThe correct answer is Va = 4.3 m/s

Hi guys, really confusing myself over grasping this principle... I think my main problem is understanding datums and how choosing the direction of a positive axis effects the result. I understand that the work energy principle states: Wnet = ½m(vf2+vi2) I have previously been taught that Wnet...
47. ### How do you derive the pV Work formula, W= "integral"pdV?

This is a Thermodynamics question. I need help in how to derive the Work done in changing from State 1 and State 2. ie: How do you derive the pV Work formula, W= "integral"dW= "integral"pdV
48. ### Understanding the Work Energy Theorem for a Spring

Hi, I looked around for hours but it seems like I'm the only one who finds it confusing. I understand the concept of potential energy and work, but have a problem with the equations. Here is what I don't understand: The work energy theorem states that K2-K1=W. W = ∫Fdx from evaluated between...
49. ### Question about work, energy and the work energy theorem.

Homework Statement So a mass m is placed on a ramp at a height given by h_1. This portion of the trip is frictionless. Then, at the bottom of the ramp the mass encounters a rough patch of levelled ground with a µk given my µ. This strip has a length of size "d" meters. After traveling across...
50. ### Bernoulli's principle and work energy theorem

for a stream line flow of ideal liquid (non-viscous) imcompressible the sum of pressure energy per unit volume kinetic energy per unit volume , potential energy per unit volume remains constant mathematically P+1/2roV2+ROGH=constant consider a fluid flowing in a pipe of various crossections we...