Equilibrium Forces: Force to Move a Mass

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Homework Help Overview

The discussion revolves around determining the forces in equilibrium for a mass subjected to tension and friction. The participants are analyzing the relationship between the normal force, tension, and frictional forces in a static equilibrium context.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants explore the relationship between the normal force and tension, questioning how changes in tension affect the normal force. There is a discussion about the maximum tension before sliding occurs and the implications of previous parts of the problem on current calculations.

Discussion Status

The conversation includes attempts to derive equations relating tension, normal force, and friction. Some participants have offered guidance on checking signs in equations, indicating a collaborative effort to clarify the problem setup. Multiple interpretations of the problem's parameters are being explored.

Contextual Notes

There is an emphasis on the dependency of the normal force on the tension, which is described as an unknown in the context of the current problem. Participants are also noting that assumptions from previous parts of the problem may not hold true in this scenario.

JoeyBob
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Homework Statement
see attached
Relevant Equations
0=Tsin(angle)+Ff
So I already know the normal force is 268.08 from a previous part of the question. I thought that the friction force must be less or equal to uFN for an object to stay in static equilibrium.

So Tcos(angle)=uFN

T=uFN/cos(angle)=116.49

But the answer is suppose to be 133.37.
 

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JoeyBob said:
So I already know the normal force is 268.08 from a previous part of the question.
But the normal force depends on the force ##T## which is an unknown.
 
TSny said:
But the normal force depends on the force ##T## which is an unknown.
T isn't an unknown. T=34
 
JoeyBob said:
T isn't an unknown. T=34
Isn't the value T = 34 N used for a previous part of the problem? In the part of the problem that you are now working on, you are looking for the maximum value that T can have before the block starts to slide. So, the value of T that you are looking for is unknown. You cannot assume that the normal force is the same in both parts of the problem. As T is increases, N increases.
 
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TSny said:
Isn't the value T = 34 N used for a previous part of the problem? In the part of the problem that you are now working on, you are looking for the maximum value that T can have before the block starts to slide. So, the value of T that you are looking for is unknown. You cannot assume that the normal force is the same in both parts of the problem. As T is increases, N increases.

So FN=mg-Tsin(angle).

Ff=umg-uTsin(angle)

0=Tcos(angle)-umg+uTsin(angle)

T=umg/(cos(angle)+usin(angle))

This gives me 94.65, which is still wrong.
 
JoeyBob said:
So FN=mg-Tsin(angle).
Check the signs in this equation. Otherwise, things are looking good.
 
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TSny said:
Check the signs in this equation. Otherwise, things are looking good.
Thanks
 

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