Understanding Magnetic Force and Weight in a Cylindrical Container

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Homework Help Overview

The discussion revolves around a problem involving the forces acting on magnets placed in a cylindrical container, specifically focusing on the reading of an analytical balance when one magnet is on the balance and another is suspended above it. The subject area includes concepts of magnetic force, weight, and Newton's laws of motion.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the forces acting on the magnets, including weight and magnetic force, and question why the balance reading is equal to the weight of one magnet rather than more. There is also discussion about the implications of Newton's third law in this context.

Discussion Status

Some participants have provided insights into the forces involved, with one suggesting that the reading of the balance could be greater than the weight of the magnet due to the interaction of forces. Others have confirmed this line of reasoning, indicating a productive exploration of the problem.

Contextual Notes

There is a lack of clarity regarding the setup of the magnets and the assumptions about the forces acting on them, particularly concerning the nature of the magnetic forces and their interaction with the balance.

elitewarr
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Homework Statement


Placed in a cylindrical container of negligible mass, a magnet with weight W is placed on a analytical balance. Another magnet is placed on top of it, hanging in mid-air and is stationary. What is the reading of the analytical balance?


Homework Equations





The Attempt at a Solution


By drawing the free-body diagram, the magnet on top will have weight acting downwards and magnetic force upwards. The magnet below will experience weight downwards, normal reaction force up wards and magnetic force downwards. I know the magnetic force must = W since the magnet is not moving. However, why is the reading of the balance = W, and not >W?

Thanks.
 
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what do u mean by hanging in mid air? is it only balanced by the repulsive force against weight or it is hanging by some rope or anything?
 
It is only balanced by the repulsive force against weight.
 
elitewarr said:

Homework Statement


Placed in a cylindrical container of negligible mass, a magnet with weight W is placed on a analytical balance. Another magnet is placed on top of it, hanging in mid-air and is stationary. What is the reading of the analytical balance?

The Attempt at a Solution


By drawing the free-body diagram, the magnet on top will have weight acting downwards and magnetic force upwards. The magnet below will experience weight downwards, normal reaction force up wards and magnetic force downwards. I know the magnetic force must = W since the magnet is not moving. However, why is the reading of the balance = W, and not >W?

Thanks.
You're correct that the magnetic force is W. To answer the question, figure out the force that the balance exerts on the weight+cylinder -- that will be the reading of the balance.

Hint: your suspicion that the reading is >W is correct.
 
But, if I'm not wrong, there's Newton's third law. The magnetic force will also be exerted on the bottom magnet. So, there's the W of the magnet, and magnetic force W acting downwards as well. Doesn't this mean that total normal reaction exerted by balance will be 2W?
 
Yes, 2W is right.
 
Oh. Okay Thanks :D
 

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