Calculating work not given acceleration, work done by gravity

In summary, the rope does work on the mass by applying a force of 20kg over a distance of 80cm, resulting in a work of 16J. On the other hand, gravity does not do any work on the mass as the mass does not move in the direction of the gravitational force. Therefore, the work done by gravity is zero.
  • #1
KinjaMSTR
1
0

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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  • #2
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.
 

1. How do you calculate work without knowing acceleration?

Work is defined as the product of force and displacement, so to calculate work without knowing acceleration, you can use the formula W = Fd, where W is work, F is force, and d is displacement.

2. What is the formula for calculating work done by gravity?

The formula for calculating work done by gravity is W = mgh, where W is work, m is the mass of the object, g is the acceleration due to gravity, and h is the vertical displacement of the object.

3. Can work done by gravity be negative?

Yes, work done by gravity can be negative if the displacement and the force of gravity act in opposite directions. This means that the object is moving in the direction opposite to the gravitational force.

4. Is work done by gravity always constant?

No, work done by gravity can vary depending on the height and mass of the object. For example, an object with a greater mass will require more work to be lifted to a certain height compared to an object with a smaller mass.

5. How is work done by gravity related to potential energy?

Work done by gravity is directly related to potential energy. When work is done by gravity, it is converted into potential energy. This means that the higher an object is lifted, the greater its potential energy will be.

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