What is Work problem: Definition and 162 Discussions

Proof of work (PoW) is a form of cryptographic zero-knowledge proof in which one party (the prover) proves to others (the verifiers) that a certain amount of a specific computational effort has been expended. Verifiers can subsequently confirm this expenditure with minimal effort on their part. The concept was invented by Cynthia Dwork and Moni Naor in 1993 as a way to deter denial-of-service attacks and other service abuses such as spam on a network by requiring some work from a service requester, usually meaning processing time by a computer. The term "proof of work" was first coined and formalized in a 1999 paper by Markus Jakobsson and Ari Juels. Proof of work was later popularized by Bitcoin as a foundation for consensus in permissionless blockchains and cryptocurrencies, in which miners compete to append blocks and mint new currency, each miner experiencing a success probability proportional to their computational effort expended. PoW and PoS (proof of stake) are the two best known Sybil deterrence mechanisms. In the context of cryptocurrencies they are the most common mechanisms.A key feature of proof-of-work schemes is their asymmetry: the work – the computation – must be moderately hard (yet feasible) on the prover or requester side but easy to check for the verifier or service provider. This idea is also known as a CPU cost function, client puzzle, computational puzzle, or CPU pricing function. Another common feature are built-in incentive-structures that reward allocating computational capacity to the network with value in the form of money.
The purpose of proof-of-work algorithms are not proving that certain work was carried out or that a computational puzzle was "solved", but deterring manipulation of data via the specific solution of establishing large energy and hardware-control requirements for the ability to do so.

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1. Can You Help Solve This Generalized Work Problem with an Illustrative Image?

Here is an image for better illustration, I only managed to solve for (a) but I'm not sure if I did it right. As for (b) and (c), I have no idea how to do it. My answer for (a): => Ki + Ui + Wext = Kf + Uf => 0+mgh1-LμmgCosΘ = 1/2mv^2 + mgh2 =>1/2v^2 = gh1- gh2 - LμgCosΘ => V = √2g(h1 - h2 -...
2. Thermodynamics: Internal Energy, Heat and Work Problem

Well, internal energy is the sum of the kinetic and potential energies of all the molecules within a given mass of a substance; this energy is associated with the random, disordered motion of the molecules. An example of internal energy is compressed gases; since gases occupy the total volume...
3. Simple Work Problem Disagreeing with Kinematics

I have the following problem: "A box with a mass of 10 kg is accelerated by 10 m/s/s over a distance of 10 meters. What is the kinetic energy of the box (assuming no friction)" Using work... Work = K.E. F * D = K.E. m*a*D = K.E. = 10 kg * 10 m/s/s * 10 m = 1000 Joules However, using...
4. Work Problem: Spring and Friction, find final Speed

First calculated non conservative work from friction using Ff=umg. Non conservative work was -8.82. Initial kinetic energy, 1/2mv^2, was 136.89. Change in potential energy, 1/2k(x)^2, was 8.1216. Ekf-Eki+Change Ep=Work NC Ekf=W NC+Eki-change Ep =-8.82+136.89-8.1216=119.9484 Ekf=1/2mv^2...
5. Conservation of energy / work problem

If someone could advise what I've done wrong it would be much appreciated. How have they eliminated the initial and final for y, and simplify only to y? Also, how did they simplify to a positive 2? What algebraic steps have I missed? Thanks for your help.
6. Work Problem -- Wood Block Sliding into a Spring

W_net = Integral from 0 to 0.70 meters [ - F_spring - F_friction ] = 1/2 * (-k) * x^2 - mu * mg * normal force * x = 1/2 * (-325N/m) * (.70)^2 - 0.250 * 6kg * 9.81m/s^2 * 0.70 - 0 = - 89.93 Joules Is this correct and am I setting this whole thing up correctly? The negative signs have me...
7. Need help on a work problem -- Pushing a shoe box up a ramp

Homework Statement A constant force (Fa) of magnitude 82.0 N is applied to a 3.00 kg shoe box at an angle of 53.0 degrees, causing the box to move up a frictionless ramp at a constant speed. How much work is done on the box by Fa when the box has moved through a vertical distance h = 0.150 m...
8. Work Problem: 3 kg Brick Falling 15 m - 441 J?

Homework Statement How much work does gravity do when a 3 kg brick falls 15 m? Homework Equations W=Fx? The Attempt at a Solution I transferred the mass of the brick to weight (gravitational force) and got 29.4. I used this number for the force and the 15 for distance, or x. Does 441 J make...
9. L

Kinetic Energy & Work Problem -- Tractor Pull Competition

Homework Statement Homework Equations W = ΔKE W = KEf-KEi The Attempt at a Solution W = .5mvf2 -.5mvi2 I know that final KE for A is 4 times the KE of B because for A ... KEf = 1/2 m (2v)^2 4KE = 1/2 m v ^2 for A I don't know what initial KE for both of them are... so how do i know if that...
10. F

Work problem involving a variable force

Homework Statement A CD case slides along a floor in the positive direction of an x-axis while an applied force Fa acts on the case. The force is directed along the x-axis and has the x component Fax = 7.0x – 2.0x^2, with x in meters and Fax in Newtons. The case starts at rest at the position x...
11. S

Work Problem - Distance of particle moving up an incline

Homework Statement Hi! I'm having issues with this practice problem. Any advice on what I'm doing wrong would help! A 2.5 kg particle is projected with an initial speed of 3.3m/s along a surface for which the coefficient of friction is 0.7. Find the distance it travels given that the particle...
12. Work problem -- raising a chain and load

Homework Statement Consider a 40-foot chain that weighs 4 pounds per foot hanging from a winch 40 feet above ground level. Find the work done by the winch in winding up the entire chain with a 600-pound load attached to it. Homework EquationsThe Attempt at a Solution ##\displaystyle...
13. Work problem -- lifting water out of tanks

< Mentor Note -- thread moved to HH from the technical math forums, so no HH Template is shown > I've encountered 2 problems in a row that involve lifting water out of tanks and finding the work needed. I am getting the incorrect answer. w = ⌠ab pgA(y)D(y)dy here is one of the problems: A...
14. Solve Flight Attendant's Work Problem: A, B & C

[Mentor note: Misplaced homework thread moved from technical forum, hence no template shown] A flight attendant pulls her 70N flight bag a distance of 253 meters along a level airport floor at a constant velocity. The force she exerts is 40 Newtons at an angle of 52 degrees above the...
15. Work problem - Rope, pulley and brick (applied integration)

If a brick is pulled across the floor by a rope thruogh a pulley, 1 meter above the ground - and work = W, where W = 10N , (in Newton).Show that the horizontal component of W, which is pulling the brick has the size \frac{10x}{\sqrt{1+x^2}} (*) Use this to calculate the amount of work needed...
16. Work problem: force vs distance curve for compound bow

Homework Statement A compound bow in archery allows the user to hold the bowstring at full draw with considerably less force than the maximum force exerted by the string. The draw force as a function of the string position x for a particular compound bow is shown in (Figure 1) . Part A How...
17. A child pulls a wagon by the handle along a flat sidewalk.

Homework Statement A child pulls a trolley by the handle along a ﬂat sidewalk. She exerts a force of 80.0 N at an angle of 30.0° above the horizontal while she moves the wagon 12 m forward. The force of friction on the trolley is 34 N. Homework Equations (a) Calculate the mechanical work done...
18. Calculating Work Done on a Particle Using Basic Formulas

Homework Statement A single force acts on a 3.3 kg particle-like object in such a way that the position of the object as a function of time is given by x = 2.1t - 1.4t2 + 1.7t3, with x in meters and t in seconds. Find the work done on the object by the force from t = 0 to t = 4.8 s. Homework...
19. Solving Work Done by Pushing a Lawnmower

Homework Statement A man pushes a lawnmower with a force of 200N. If the vertical component of this force is 80N how much work is done in pushing the lawnmower 6.0m horizontally? Homework Equations Work=force x distance The Attempt at a Solution Firstly I have to find the angle to the ground...
20. Work problem, box moves at h=.25 with F=85N

Homework Statement A constant force Fa of magnitude 85.0N is applied to a 3.0kg shoe box at angle 55.0, causing the box to move up a frictionless ramp at constant speed. How much work is done on the box by Fa when the box has moved through vertical distance h=.25m? Homework Equations...
21. Physics force and work problem

Homework Statement A 65-kg worker at a bakery loses his balance and falls 4.0 m before hitting the surface of a large vat of cake batter. He continues to travel downwards an additional 2.0 m before the cake batter finally brings him to rest. Calculate the work done on the worker by the cake...
22. Solve Simple Work Problem: Steve + 30° + 0.20 μ

Homework Statement A 50 KG box was dragged across a floor for a distance of 20 meters at a constant velocity by Steve pushing on the box at an angle of 30 degrees below the horizontal. If the coefficient of kinetic friction between the box and the floor is 0.20, calculate the work he did...
23. Calculating Work Done on a Hanging Chain Using Mass Density and Length

A 3.0m long steel chain is stretched out along the top level of a horizontal scaffold at a construction site, in such a way that 2.0 m of the chain remains on the top level and 1.0m hangs down vertically. At this point ( the 1.0m segment that is hanging) is sufficient to pull the entire change...
24. With This Integral. Not Home Work Problem

Homework Statement Actually I have the problem solved but I do not understand how the numerator becomes equal to the denominator in the 3rd step. Homework Equations I have been looking for an identity for arctan but can't find one that seems to match. The Attempt at a Solution My attempt...
25. Kinetic energy and work problem

Homework Statement In the figure here, a block of ice slides down a frictionless ramp at angle θ=55.0 ˚ while an ice worker pulls on the block (via a rope) with a force that has a magnitude of 54.0 N and is directed up the ramp. As the block slides down through distance d = 0.400 m along the...
26. Formula for relating time and heat gained for closed system

This is for work. I need to make a table for a client. What we did: had two different closed systems, only difference is material. We had frozen goods in both containers, the containers were both removed from the cooled surroundings they were in and placed outside. The temperatures were...
27. Solve Tricky Work Problem: Find Combined Effort Time

1. A works alone, takes 4 days more to complete the job than if both A and B do together. If B works alone, he takes 16 more days than the situation of working together. The question asks to find how many days it takes for the combined effort, which being apparently simple has unfortunately made...
28. Am I underthinking this work problem?

Homework Statement A mass m is dropped from rest above a relaxed spring of stiffness k a distance D. Find the position from where it was released where the mass attains its maximum velocity and find that maximum velocity Homework Equations W_{net}=\Delta E The Attempt at a Solution ok... so...
29. Why isn't the force in the direction of the velocity in the equation F=P/v?

Homework Statement See attached imageHomework Equations See attached imageThe Attempt at a Solution See attached image I simply want some guidance pertaining to if I did this problem correctly. Is the diagram correct? In addition, I have a specific question. We have the equation ##\vec{F} =...
30. Solving Simple Work Problem: 515J

Homework Statement A 70.0 kg sailor climbs an 11.5 m long rope ladder to a mast above at constant velocity. The rope ladder is at an angle of 30.0° with the mast. Assume that the ladder is frictionless. How much work does the sailor do? Homework Equations ##W = Fd##The Attempt at a Solution...
31. Calculating Force Needed to Pull Chain Onto Table

Homework Statement Homework Equations W = F d F = ma The Attempt at a Solution so in order to get the whole chain on the table, we need to pull the chain 0.65 meters onto the table. since 0.65 meters is hanging off the table, the gravity is acting on it, therefore F=ma where m is half the...
32. Center of earth Work problem (some calculus)

Homework Statement The force of attraction on an object below Earth's surface is directly proportional to it's distance from Earth's center.Find the work done in moving a weight of ##w## lb located ##a## miles below Earth's surface up to the surface itself. Assume Earth's radius is a constant...
33. Kinetic Energy and Work problem

Homework Statement [/B] A horizontal force of 50 N is applied to a 2.0 kg trolley, initially at rest, and it moves a distance of 4.0 m along a level, frictionless track. The force then changes to 20 N and acts for an additional distance of 2.0 m. (a) What is the final kinetic energy of the...
34. Direction of motion climbing up stairs for work problem

I wanted to know why the we calculate the work done of a person climbing up a set of stairs using the y direction,for example, we use the equation w=mgh to calculate the work done for a person climbing up a set of stairs. I do not understand why we are not also calculating the work done in x...
35. Work problem -- Steam piston volume and work length

Homework Statement Steam is raised as saturated steam at 6 bar (g) and supplied to the first ( high pressure ) piston. The steam then exhausts from piston 1 at 3 bar (g). The steam is thought to expand adiabatically in accordance with PV^( 135 .1)= Constant Given the initial volume is...
36. What are the steps to solve a work problem?

I know there isn't a "set in stone" step by step procedure to solve work problems, but if someone could give me a basic procedure it would be greatly appreaciated. When ever I read a work problem, unless it is a simple "plug in the value" works equation problem, I do not understand how to start...
37. Change in Electric potential, potential energy, and work problem.

Homework Statement Imagine a lithium atom where the two electrons in the first orbital are at exact opposite sides of the nucleus and the electron in the second orbital is in line with the other electrons so that the three electrons and the nucleus all lie on a straight line. How much work...
38. Work problem, physics solution

I work at a nursery in California where we go out and plant the trees that we sell. Some of these trees are in 36" boxes and weigh up to 1700 lbs. Many times customers have 3-5 feet retainer walls and don't want to pay for a crane, and the planting crew is forced to hand lift these boxes inch by...
39. How Do You Calculate Work Done on a Particle Given Its Position-Time Equation?

I was given the problem: A single force acts on a 3.6 kg particle-like object in such a way that the position of the object as a function of time is given by x = 4.1t - 0.64t2 + 2.0t3, with x in meters and t in seconds. Find the work done on the object by the force from t = 0 to t = 8.1 s...
40. Time & Work Problem: Solving 1/2 Unit of Work in 6 Days

Homework Statement Q. 2 Men working 3 hours/day works for 4 days to complete a work (unit of work). Calculate how many days required by 1 man working 2 hours/day to complete the 1/2 of that work ?Homework Equations ## \frac{M_1H_1}{W_1} = \frac {M_2H_2}{W_2}##The Attempt at a Solution Sol...
41. Calculating Work Done by Friction?

Homework Statement A 3-kg block is moved up a 37° incline under the action of a constant horizontal force of 40 N. The coefficient of kinetic friction is .1, and the block is displaced 2 m up the incline. Calculate (a) the work done by the 40-N force, (b) the work done by gravity, (c) the work...
42. Solving the Hardest Work Problem Homework

Homework Statement A bucket of water with mass 100kg is on the ground attached to one end of a cable with mass per unit length of 5kg/m. The other end of the cable is attached to a windlass 100m above the bucket. if the bucket is raised at a constant speed, water runs out through a hole in...
43. Work Problem - Pushing a lawnmower

Work Problem -- Pushing a lawnmower 1. A lawn mower (25kg) is pushed a horizontal distance of 10m by a 50 N downward force directed 60 degrees to the horizontal. The coefficient of kinetic frictional force is .017. What is the work done by each of the external forces on the lawn mower...
44. What is the Young's modulus of a nylon rope used for climbing?

Homework Statement For safety climbing, a mountaineer uses a nylon rope that is 41m long and 0,4 cm in diameter. When supporting a 97kg climber, the rope elongates 1,8m. Find its Young’s modulus. The acceleration of gravity is 9,8 m/s2 a) 82,46 x 108 Pa b) 17,18 x 108 Pa c) 25 x 106...
45. Solving Energy Work Problems: Examples #1 & #2

Hi, I was wondering if anyone could please help me understand when is there no work in Joules being produced when your object is moving at a constant velocity. Example #1: Brenda carries a 5.0 kg suitcase as she walks m along a horizontal walkway to her room at a constant speed of 6.5 m/s...
46. Troubleshooting a Virtual Work Problem

https://www.physicsforums.com/attachment.php?attachmentid=65907&stc=1&d=1390369310 I've been stuck on doing my revision on this problem. The equation of the virtual work, from what I deduce is [du = 0] -Pdx + mg dh However the answer given is...
47. Work problem on grocery cart

A shopper pushes a grocery cart 20.0 m at constant speed on level ground, against a 35.0 N frictional force. He pushes in a direction 25.0º below the horizontal. Find the force the shopper exerts, using energy considerations. I got stuck on this because they don't give the mass of the cart.
48. Power and Speed Relationship for Lifting Objects

Homework Statement The maximum power your body can deliver in lifting an object vertically is 78 W. How fast could you lift, at constant speed, a 2L full water container? P=78W m=2kg t=? v=? Homework Equations P=ΔE/t E=1/2mv2 The Attempt at a Solution 78W=(.5*m*v2)/t...
49. Orientation on Calculus Work Problem. Hooke's Law.

A force of 16,000lb compresses a string from its natural length of 13 inch to 8 inch. Find the work done to compress it to the first inch W=$$\int F dx$$ F=kx 16000=K(5) 3200=KW=$$\int F dx$$ W=$$\int_1^{13}\!\ 3200xdx$$ [1600x^2] from 1 to 13 w= 268800ftlb Am I right? I think the trick...
50. Work problem on winding up a cable

Find the work done in winding up a 300ft cable that weighs 2.00 lb /ft W=Fd W=$$\int F dx$$ My attempt w=F*D so W= (300ft)(2.00lb/ft) W=600ft.lb and $$\int_0^{300}\!\ 2xdx$$ W=90,000 ft.lb I'm taking Calc 2 and this is applied Physics problems...