Calculating work not given acceleration, work done by gravity

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SUMMARY

The discussion focuses on calculating the work done by a rope lifting a 20kg mass vertically by 80cm, as well as the work done by gravity on the mass. The correct formula for work is W = FΔd, where F is the force applied and Δd is the distance moved. The work done by the rope is dependent on the force exerted, which requires knowledge of the acceleration. The work done by gravity is incorrectly calculated as zero; in fact, work is done against gravity when lifting the mass, highlighting the importance of energy conservation in the process.

PREREQUISITES
  • Understanding of Newton's laws of motion
  • Familiarity with the work-energy principle
  • Knowledge of gravitational force calculations (Eg = mgh)
  • Basic algebra for manipulating equations
NEXT STEPS
  • Calculate work done using W = FΔd for various forces and distances
  • Explore the concept of energy conservation in mechanical systems
  • Learn about different types of forces and their impact on work done
  • Study the implications of acceleration on work calculations
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Students studying physics, educators teaching mechanics, and anyone interested in understanding work and energy principles in physical systems.

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Homework Statement


A rope lifts a mass of 20kg vertically 80cm.

How much work is done by the rope on the mass?

How much work is done by gravity on the mass?



Homework Equations


W = FΔd
Eg = mgh


The Attempt at a Solution


How much work is done by the rope on the mass?
W = FΔd
W = F(0.8)

This is as far as I've gotten. I don't think this is the correct solution. For this to work, I would need to put the applied force of the rope. The problem is that I don't know the acceleration of the rope, so I'm thinking this may be the completely wrong approach.

How much work is done by gravity on the mass?
So far what I have is:
W = FΔd
W = mgΔd
W = (20)(9.81)(0)
W = 0

Because gravity doesn't move the mass, the work done by gravity is zero. I believe this is the correct solution.
 
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I believe this is the correct solution.
It is not.

It does not matter "what" moves the mass. The mass moves against the direction of the gravitational force, that needs work. Energy is conserved, so where does that work come from?

The speed of the process and other things don't matter, you have the correct formulas there.
 

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