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. L

    How Is Work Calculated on a Mass on a Frictionless Track?

    Homework Statement A 3.0 kg body is at rest on a frictionless horizontal air track when a constant horizontal force acting in the positive direction of an x-axis along the track is applied to the body. A stroboscopic graph of the position of the body as it slides to the right is shown in...
  2. R

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    Sam works at an amusement park. A boat of children on a water ride comes the the pier at the end of the ride. They are moving at a constant speed of 1.2 m/s, and the loaded boat has a mass of 1200kg. Sam slows the boat down by pushing on it until it comes to rest at the pier. If he stops it in a...
  3. Z

    Work problem: Pulling wagon and finding angle

    Homework Statement In many neighborhoods, you might see parents pulling youngsters in a four-wheeled wagon. The child and the wagon have a combined mass of 50kg and the adult does 2.2 x 10^3 J of work pulling the two 60m at a constant speed. The coefficient of friction for the surfaces in...
  4. T

    Simple Work problem with block and friction.

    Suppose that a 50kg block slides along a horizontal surface where the coefficient of kinetic friction between the block and the surface is 0.60. A force F = 400 N is now applied where the angle of the force above horizontal is 20°. (Like a string pulling the block from the right 20 degrees...
  5. P

    How can pressure and volume affect the work, energy, and heat of helium gas?

    Homework Statement Imagine some helium in a cylinder with initial volume of 1 liter and an initial pressure of 1 atm. Somehow the helium is made to expand to a final volume of 3 liters, in such a way that its pressure rises in diect proportion to its volume. a) calculate the work done on...
  6. D

    Calculus Work Problem (Spherical Water Tower)

    Homework Statement A spherical water tower 40 ft in diameter has its center 120 ft above the ground. That means, there is a 120 ft pole connected to the 40 ft diameter spherical tank. Water is being pumped at the ground level to fill the tank with water of density 62.4 lb/ft3, a) How much...
  7. R

    Calculate Work Done by Gravity: Physics Homework Problem

    Homework Statement A 0.179 kg ball is thrown straight up from 1.94 m above the ground. Its initial vertical speed is 10.00 m/s. A short time later, it hits the ground. Calculate the total work done by the force of gravity during that time. m = .179 kg vi = 10m/s (upward) g = 9.8 m/s2 d =...
  8. S

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  9. K

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    Help!Work problem Homework Statement A person pulls a heavy load of mass 74kg up the side of a building using a rope and a frictionless pulley. the load travels up 34m with constant velocity. how much work is done by a)gravity b)tension in the rope c)the person diagram: ---- represents...
  10. M

    How much mechanical work was done by 2 men lifting a boat 24 times?

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  11. D

    Solving Work Problem: Kinetic Energy of Toy Car After Braking

    The toy car is sliding with a kinetic energy of 6.4 J when it locks up its tires (obviously, the toy driver slammed on the toy brakes) and slides for 62 cm, while a frictional force of 0.63 N acts against it. What is the kinetic energy (in Joules) of the car after this frictional work is done...
  12. B

    Work Problem, opposing forces (no friction)

    Homework Statement In the figure below, http://www.webassign.net/userimages/jshemwell@lincolnpark.il/Net%20Force/Two_opposing_horizontal.gif T1 = 32 N, and T2 = 19 N. The surface has no friction. The block travels a displacement of 11 m to the right as a result of these forces. a. What is the...
  13. D

    Calculating Elevator Motor Work: 500 kg Lifted 50 m | Urgent Problem Solution

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  14. C

    How Is Work Calculated in an Elevator Physics Problem?

    Homework Statement A 0.250 kg block of cheese lies on the floor of a 900 kg elevator cab that is being pulled upward by a cable through distance d1 = 2.40 m and then through distance d2 = 10.5 m. (a) Through d1, if the normal force on the block from the floor has constant magnitude FN = 3.00...
  15. B

    Is My Solution for Variable Force Particle Motion Correct?

    Homework Statement A particle of mass m starts from xo= 0m with vo> 0 m/s. The particle experiences the variable force Fx= Fosin(cx) as it moves to right along the x-axis, where Fo and c are constants. a)At what position xmax does the force first reach a maximum value? b) What is the...
  16. K

    Moment of intertia and net work problem

    A ballerian spins initially at 1.5rev/s when arms are extended. She then draws in her arms to her body and her moment of intertia is .88kg m^2 and her angular speed increases to 4.0rev/s. Determine the network she did to increase her angular speed? To find moment of inertia was pretty simple...
  17. T

    Net Work Problem, Rotational Motion,

    A ballerian spins initially at 1.5rev/s when arms are extended. She then draws in her arms to her body and her moment of intertia is .88kg m^2 and her angular speed increases to 4.0rev/s. Determine the network she did to increase her angular speed? So i first needed to solve for the initial...
  18. M

    Energy/ work problem set(last question )

    Energy/ work problem set(last question!) Homework Statement A 53.5 g ice cube can slide without friction up and down a 33.0° slope. The ice cube is pressed against a spring at the bottom of the slope, compressing the spring 12.0 cm. The spring constant is 22.0 N/m. When the ice cube is...
  19. G

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  20. E

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    Homework Statement An old oaken bucket of mass 6.75 kg hangs in a well at the end of a rope. The rope passes over a frictionless pulley at the top of the well, and you pull horizontally on the end of the rope to raise the bucket slowly a distance of 4.00m. (a) How much work do you do on the...
  21. P

    Finding Velocity in Work Problem

    [SOLVED] Finding Velocity in Work Problem I've already solved A and B and I used W = Fxcos(theta) but that has nothing to do with velocity. Can someone please help me on C and D.
  22. A

    How Do You Calculate Force and Work for Lifting a Box onto a Dock?

    Homework Statement A 35kg box needs to be lifted to the top of a loading dock, which is also accessibly by ramp. The ramp is 5.0m long and has a vertical height of 1.7m. a) What minimum force is required to lift the box straight up onto the loading dock? b) What minimum amount of work is...
  23. S

    How Much Work is Done When Pushing a Sled with Different Friction Forces?

    Homework Statement A girl pushes her little brother on his sled with a force of 300N for 750m. How much work is done if the force of friction is a) 200N and b) 300N? Homework Equations W = F \Delta x The Attempt at a Solution F_{net} = F_p - F_f F_{net} = 300N - 200N = 100N...
  24. R

    Tony Pulls Wagon: Work Problem Solutions

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  25. M

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  26. J

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  27. O

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    Homework Statement BlimpWork A blimp of mass 100 kg is pulled at an angle \phi = 27^{o} downwards with respect to the horizontal for d = 10 km on level ground at a constant velocity v = 12 m/s. If the coefficient of drag (K in F = Kv^2) is 0.5 kg • m, how much work in Joules is done by the...
  28. H

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    Homework Statement A person pushes a 10.0 kg mass up a 7.60 m long, 20 degree ramp( mu=.170) with a horizontal force of 70.0N. Find the work done by the person and the heat energy generated by friction. the answer for heat energy i canot get..its supposed to be 150J Homework Equations...
  29. H

    Solve for the Maximum Incline | Car Acceleration & Power Problem

    Homework Statement A 1100kg car can accelerate from 0-60kph in 6.5 seconds. With constant engine power, what is the steepest hill the car could climb at 20 kph. Homework Equations F=ma W=Fd P=W/t g=mgSin(theta) maybe work energy theorem? The Attempt at a Solution Not Much...just...
  30. L

    Solve a Simple Work Problem and Find Out Why You're Wrong

    Hello :) I must have missed something. This problem is extremely simple and yet I can't figure out what I'm doing wrong. Really frustrating! The problem: A bucket of mass 6.75 kg hangs in a well at the end of a rope. The rope passes over a frictionless pulley at the top of the well, and you...
  31. L

    Calculating Normal Force, Acceleration, and Work in a Force and Work Problem

    A child pulls a 15kg sled containing a 5kg dog along a straight path on a horizontal surface. He exerts a force of a 55N on the sled at an angle of 20 degree above the horizontal. The coefficient of friction between the sled and the surface is 0.22 . Find:a) normal force of the surface on the...
  32. D

    How Does Friction Affect the Distance a Block Slides on an Elevated Track?

    Homework Statement A small block slides along a track from one level to a higher level, by moving through an intermediate valley (see Figure). The track is frictionless until the block reaches the higher level. There a frictional force stops the block in a distance d. Assume that the block's...
  33. P

    Calculating Work and Force: A Factory Worker's Challenge Solved!

    A factory worker pushes a crate of mass 28.5 kg a distance of 4.70 m along a level floor at constant velocity by pushing horizontally on it. The coefficient of kinetic friction between the crate and floor is 0.25. What magnitude of force must the worker apply? How much work is done on...
  34. L

    Isothermal and reversible expansion work problem (Physical Chem)

    Homework Statement A sample of 2.00 mol. CH3OH (g) is condensed isothermally and reversibly to liquid at 64*C. The standard enthalpy of condensation of methanol @ 64*C is -35.3 kJ/mol. Find w and q for the reaction. Homework Equations w = -nRT * ln(Vf/Vi) (although I don't have volume...
  35. B

    Setting up a work problem. pumping gasoline

    I just have a quick question. I'm supposed to find the work required to pump gas out of a cone, but am having trouble finding the radius of the cone. The cone measures 10 feet in height. I broke it up and set it up using similar triangles, and this is what I got: It doesn't seem right...
  36. H

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    Homework Statement Suppose you throw a stone having a mass of 0.50 kg vertically upward. Let us assume that your hand exerts an average force of 110 N over an arm displacement (upward) of 0.60 m. Through the following sequence of questions, we shall explore, in terms of the energy and...
  37. R

    Calculating Work and Force in a Perfectly Inelastic Collision

    Homework Statement A car of mass 1240 kg has kinetic energy of 116 kJ. There is a stalled SUV of mass 2710 kg blocking the intersection. Because he obliviously chatting away on his cell phone, the driver of the car plows into the SUV without braking. The two vehicles stick together (a...
  38. tony873004

    Work problem. Right answer, wrong units

    My answer should obviously be in Newtons, but I'm getting Netwon meters. An aquarium, 2 m long, 1 m wide, and 1 m deep is full of water. Find the work needed to pump half the water out of the aquarium. (The density of water is 1000 kg/m3.) In a similar example in the book, they do the...
  39. W

    Work Problem, Line Integral Fun (Calc 3)

    Homework Statement Find the work done by the force field F(x,y) = x*sin(y) i-hat + y j-hat on a particle that moves along the parabola y = x^2 from (-1,1) to (2,4). 2. The attempt at a solution Please see attached file. The answer I get seems really, really, complicated and I have a...
  40. L

    Solving a Physics Problem: How Far Will the Ball Land?

    Ok here's the problem: A batter hits a ball which leaves the bat 1 meter above the ground at an angle of 65 degrees with an initial velocity of 30 m/s. How far from home plate will the ball land if not caught and ignoring any air resistence? So I tried solving for how much of the velocity is...
  41. W

    Calculate Average Power: 60kg Woman Running Up 4m Stairs in 6s

    not sure how to solve this, having trouble finding the equation I need in my book. any help is appreciated. thanks in advance. A 60 kg woman runs up a flight of stairs having a rise of 4.0 m in a time of 6.0 s. What average power did she supply?
  42. M

    HELP ON A WORK PROBLEM CAN'T DO IT BY MYSELF SNIFF SNIFF.:cry:

    a uniform ladder of mass 12kg is 4.6m long. if it is lifted from a horizontal to a vertical position, how much work is done i just thought because i have to lift the centre of the mass, i'd have to do mgh with h being 2.3m. I think i am sure that i don't have the right answer. Sniff.. help...
  43. B

    How Long Will It Take for the Rescue Ship to Reach You?

    You are sitting in a life boat at rest on a calm se, with your eye 1m above the water. A rescue ship is moving directly toward you at a constant speed of 5m/s. If the tallest point on the ship is 12m above the water, how long will the ship take to reach you from the moment when you can first see...
  44. K

    How Much Work is Needed to Pull a Skier Up a Slope?

    a skier of mass 72.9 kg is pulled up a slope by a motor-driven cable. The acceleration due to gravity is 9.81 m/seconds squared. How much work is required to pull the skier 63.5 m up a 34 degree slope (assumed to be frictionless) at a constant speed of 2 m/seconds squared. Answer in units of J...
  45. V

    Need Help with Physics Homework? Learn How to Solve a Simple Work Problem Here!

    Hi everyone. I just found this forum and it looks like a good place to get some help on my physics homework. Anyways, this year, I have bad luck. I have a REALLY bad physics teacher (I'm not bashing on teachers here, but it's true). He doesn't do anything; we haven't learned ANYTHING from his...
  46. J

    How Do You Calculate Work Done by a Variable Force Along a Displacement?

    A single conservative force acts on a 5.00 kg particle. The equation Fx = (2x + 4) N describes this force, where x is in meters. As the particle moves along the x-axis from x = 2.60 m to x = 6.20 m, calculate the following. (a) the work done by this force ----------------- Alright this seems...
  47. J

    Work problem of person pushing box

    hi, Please help me with this problem, thanks. Harry pushes a box (that weighs 98 N) with a force of 20 N on ice. After he stops pushing the box is still in motion. The kinetic energy of the box is 20 J and the coefficient of friction is .05. Find a) Mass of the box? b) Force of friction...
  48. K

    Why Is My Calculation of Speed on an Inclined Plane Incorrect?

    This problem is giving me issues. I don't think I'm using the right equations... Problem: A 2.0-kg mass is released from rest at the top of a plane inclined at 20 degrees above horizontal. The coefficient of kinetic friction between the mass and the plane is 0.20. What will be the speed...
  49. C

    Piano sliding down an incline - work problem

    Hi, could someone please help me? Here is the problem: "A 265 kg piano slides 4.6 m down a 30° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. (a) Calculate the force...
  50. W

    Solve Work Problem: Friction & Sliding Distance of 62 kg Player in Baseball Game

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