Tension variation in a rotating rope

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Homework Statement


A uniform rope with length L and mass m is held at one end and
whirled in a horizontal circle with angular velocity You can
ignore the force of gravity on the rope. (a) At a point on the rope a
distance r from the end that is held, what is the tension F?

Homework Equations


(Wave´s speed)=(lambda)*(Frenquency)
(Wave´s speed)=((Tension)/(Mass per unit lenght))^(1/2)

The Attempt at a Solution


I don´t know how to start, how does the tension vary along the rope? can somebody give me a hint of how the tension vary along the rope?
 

Discussion

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Well, I'm by no means an expert, but doesn't centripetal force exerts an influence? When you whirl the rope in a horizontal circle, centripetal force on a portion of the rope will change in function of the distance r from the end that is held - the radius of the circle changes.

EDIT: Do your question is related somehow to slide 6 in this link?
http://www.iitg.ac.in/asil/Lecture-4.pdf
 
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What made you think this question involved waves?

sebas said:
I don´t know how to start, how does the tension vary along the rope? can somebody give me a hint of how the tension vary along the rope?
Imagine a simpler case; a stationary hanging rope. At the top the rope supports the entire weight of the rest of the rope so tension is at it's maximum, at the bottom tip it's supporting no weight at all so the tension is zero.
The same applies to your rotating rope. Draw a free body diagram,You must make the simplifying assumption that the rope is straight and radial*.
Apply Newtons laws, solve for T as a function of r.

*For bonus points:can you predict/experiment what an actual rope would do? What shape would it assume? Do you have enough information to solve for that much more complicated case?
 
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billy_joule said:
What made you think this question involved waves?Imagine a simpler case; a stationary hanging rope. At the top the rope supports the entire weight of the rest of the rope so tension is at it's maximum, at the bottom tip it's supporting no weight at all so the tension is zero.
The same applies to your rotating rope. Draw a free body diagram,You must make the simplifying assumption that the rope is straight and radial*.
Apply Newtons laws, solve for T as a function of r.

*For bonus points:can you predict/experiment what an actual rope would do? What shape would it assume? Do you have enough information to solve for that much more complicated case?

Actually, looks like this question is in a chapter about mechanical waves in some physics textbook:
http://web.uvic.ca/~jalexndr/295Ch15YFproblems.pdf
Anyway, is the case you mentioned related to the link I posted?
http://www.iitg.ac.in/asil/Lecture-4.pdf
 
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ramzerimar said:
Actually, looks like this question is in a chapter about mechanical waves in some physics textbook:
http://web.uvic.ca/~jalexndr/295Ch15YFproblems.pdf
Anyway, is the case you mentioned related to the link I posted?
http://www.iitg.ac.in/asil/Lecture-4.pdf
The problem is from the chapter about mechanical waves, I don't think it is somewhat related to the link you posted
 
ramzerimar said:
Actually, looks like this question is in an chapter about mechanical waves in some physics textbook:
http://web.uvic.ca/~jalexndr/295Ch15YFproblems.pdf

Yes. But the the OP hasn't made it to b) or c) so waves aren't relevant yet.

sebas said:
The problem is from the chapter about mechanical waves, I don't think it is somewhat related to the link you posted

It isn't somewhat related to the link, the link shows the exact solution to your problem!
The only difference is they use 'M' to represent the mass where as you will use 'm'.

Forget about waves for now, you are looking for tension as a function of r.
Have you made any attempt? A free body diagram? Applied Newtons laws?
 
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billy_joule said:
Yes. But the the OP hasn't made it to b) or c) so waves aren't relevant yet.
It isn't somewhat related to the link, the link shows the exact solution to your problem!
The only difference is they use 'M' to represent the mass where as you will use 'm'.

Forget about waves for now, you are looking for tension as a function of r.
Have you made any attempt? A free body diagram? Applied Newtons laws?
Tension as a function of r is: F=(m/L)*(L-r)*g; right?
if so, how the presence of waves can affect the tension in the rope?
 
sebas said:
Tension as a function of r is: F=(m/L)*(L-r)*g; right?
No, you were told to ignore gravity. Where did you get that equation from?
sebas said:
how the presence of waves can affect the tension in the rope?
As billy_joule says, the question you posted has nothing to do with waves.
 
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haruspex said:
No, you were told to ignore gravity. Where did you get that equation from?

As billy_joule says, the question you posted has nothing to do with waves.
haruspex said:
No, you were told to ignore gravity. Where did you get that equation from?

As billy_joule says, the question you posted has nothing to do with waves.
Sorry, I hugely misunderstood the problem, I was imagining the rope with waves, confusion solved, thanks.