Stick being pulled by a string from the top

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Homework Help Overview

The problem involves a vertical stick of length 2m and weight 45.9kg, which is being pulled by a string from the top while a force of 100N acts horizontally at its midpoint. The objective is to determine the friction coefficient necessary for the stick to remain at rest.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants discuss the forces acting on the stick, including weight, tension, and friction. There are attempts to set up equations based on the conditions for equilibrium, including the sum of forces and torques. Some participants express uncertainty about the tension in the string and its implications for solving the problem.

Discussion Status

There is ongoing exploration of the relationships between the forces involved, with some participants suggesting the need for additional equations to resolve the unknowns. A drawing has been provided to aid understanding, and participants are encouraged to clarify the angle involved in the setup.

Contextual Notes

Participants note the importance of considering both linear and rotational equilibrium, indicating that the problem may require a comprehensive approach to analyze the forces and moments acting on the stick.

thonwer
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Homework Statement


We have a stick which is vertical, its length is 2m and its weight 45.9kg. A string is pulling the top of the stick from the floor at a distance of 2m from the left of the bottom of the bar. A force of 100N is pulling from the right at the middle of the stick. Which has to be the friction coefficient for the friction force acting on the bottom of the stick? The stick has to be in rest.

https://imagizer.imageshack.us/v2/800x600q90/607/kb5l.jpg

Homework Equations



F=ma
p=mg
R=u*N

u=(friction coefficient)
N=(normal reaction)
p=weight
T=tension

The Attempt at a Solution



y axis: p+Ty=N -> N=p+Tcos(Θ)

x axis: F=R+Tx ->F=uN+Tsin(Θ) -> u=(\frac{F-Tsin(Θ)}{p+Tcos(Θ)})
 
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So ?
Make a drawing.
\sum \vec F = 0 is one condition for non-movement. Any others ?
 
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I can't solve the equation, I don't know the value of T
 
I'm even worse off: I don't know what T is!
 
T is the tension of the string
 
I kind of guessed that. If you don't know it, keep it and you'll find an expression for the friction coeffient in terms of T. More can't be asked from you. In the mean time I can ask you: what is theta ?
Helper's lives are lengthened by completeness in 1. and 2. Also in 3.

Drawing ?
 
Oh the drawing I forgot I'm sorry :) I'll upload it in a minute
 
Here is the drawing

https://imagizer.imageshack.us/v2/800x600q90/607/kb5l.jpg
 
Sure helps. You even added it as a picture in post #1. Makes the thread unintelligible for later readers, but never mind. So ##\cos \theta = \sin \theta = \frac {1}{2}\sqrt 2##.
I don't think there's anything I can improve on what you've come up with so far.

However, what about T ? You know the thing isn't moving. Back to the "Any others" in post #2.
 
  • #10
You've formed one equation (still two unknowns though).

Perhaps you should take a moment*.

*(By that I don't mean "take a moment to relax and contemplate the situation," but rather I mean take a moment. Given that nothing is rotating either, it means that sum of all torques [moments] around any given point must also be zero. You can find a new equation by taking a moment around any point, however, some points may be better than others. :wink:).

[Edit: I see now that BvU is back. :smile:]
 
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