What is the Force Exerted by the Ground on Object 1 in an Atwood Machine?

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Homework Help Overview

The discussion revolves around calculating the force exerted by the ground on an object in an Atwood machine setup, specifically focusing on an object weighing 77.00 N and its interaction with another object of varying weights (30 N, 60 N, and 90 N). Participants explore the implications of these calculations on the system's behavior.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants discuss different approaches to calculating the force exerted by the ground, including drawing free body diagrams (FBDs) and applying Newton's second law. Questions arise regarding the validity of results, particularly concerning negative forces and the implications for the system's state.

Discussion Status

There is an ongoing exploration of the calculations and their implications. Some participants have re-evaluated their approaches based on earlier results, while others are questioning the assumptions made about the forces involved. Guidance has been offered regarding the interpretation of negative forces in the context of the problem.

Contextual Notes

Participants are considering the physical constraints of the system, such as the impossibility of the ground exerting a negative force and the conditions under which object 1 would no longer be in contact with the ground.

antonisz
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1. A 77.00 Nt object (denoted as object 1) rests on the ground. A light cord is connected to this object which runs vertically upward over a light frictionless pulley and is attached to another object denoted as object 2.

a) Calculate the force that the ground exerts on object 1 if object 2 is 30 N.

b) Calculate the force that the ground exerts on object 1 if object 2 is 60 N.

c) Calculate the force that the ground exerts on object 1 if object 2 is 90 N.



http://imgur.com/cVEQW07 http://imgur.com/cVEQW07

g (m1 - m2) / (m1) + m2 = ay I drew FBD's for both of the weights and solved for the acceleration for situation a. I then used the equation w - t = ma and solved for the tension value, I then subtracted the tension value from the original weight of object 1, and I got 33.88 N.

I feel like this is the wrong way of solving the problem because once you get to situation c, you would have a negative force which can't be possible.
 
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antonisz said:
1. A 77.00 Nt object (denoted as object 1) rests on the ground. A light cord is connected to this object which runs vertically upward over a light frictionless pulley and is attached to another object denoted as object 2.

a) Calculate the force that the ground exerts on object 1 if object 2 is 30 N.

b) Calculate the force that the ground exerts on object 1 if object 2 is 60 N.

c) Calculate the force that the ground exerts on object 1 if object 2 is 90 N.



http://imgur.com/cVEQW07 http://imgur.com/cVEQW07

g (m1 - m2) / (m1) + m2 = ay


I drew FBD's for both of the weights and solved for the acceleration for situation a. I then used the equation w - t = ma and solved for the tension value, I then subtracted the tension value from the original weight of object 1, and I got 33.88 N.

I feel like this is the wrong way of solving the problem because once you get to situation c, you would have a negative force which can't be possible.
That seems to be a correct result for part c. -- but ...

If the ground can't produce a negative (downward) force on m1, then what do you suppose happens to the system?

attachment.png
 

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SammyS said:
That seems to be a correct result for part c. -- but ...

If the ground can't produce a negative (downward) force on m1, then what do you suppose happens to the system?

attachment.php?attachmentid=71007&stc=1&d=1404148813.png

The system would change where object 1 would be "in the air" correct?
 
antonisz said:
The system would change where object 1 would be "in the air" correct?

Yes, so the ground will exert what force on m1?
 
SammyS said:
Yes, so the ground will exert what force on m1?

It would have to be 0 Newton's. If I'm correct about that, then I already assumed that, however I rethought my approach on part a and b.

I redid the FBD's for (a) and (b) and added the two equations for Newton's second law, and the tensions canceled each other out, leaving me with w1 - w2 = Fn. From there I calculated that in situation (a), the force that the ground exerts is 47 Newton's, and in situation (b) it would be 17 Newton's.
 
Last edited:
antonisz said:
It would have to be 0 Newton's. If I'm correct about that, then I already assumed that, however I rethought my approach on part a and b.

I redid the FBD's for (a) and (b) and added the two equations for Newton's second law, and the tensions canceled each other out, leaving me with w1 - w2 = Fn. From there I calculated that in situation (a), the force that the ground exerts is 47 Newton's, and in situation (b) it would be 17 Newton's.
That all looks good!
 
SammyS said:
That all looks good!

Thank you so much for the help!
 

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